diff --git a/app/auto-updater-linux.ts b/app/auto-updater-linux.ts
index da83733a..d6344fdf 100644
--- a/app/auto-updater-linux.ts
+++ b/app/auto-updater-linux.ts
@@ -21,9 +21,10 @@ class AutoUpdater extends EventEmitter implements Electron.AutoUpdater {
     this.emit('checking-for-update');
 
     fetch(this.updateURL)
-      .then((res): any => {
+      .then((res) => {
         if (res.status === 204) {
-          return this.emit('update-not-available');
+          this.emit('update-not-available');
+          return;
         }
         // eslint-disable-next-line @typescript-eslint/camelcase
         return res.json().then(({name, notes, pub_date}) => {
@@ -40,7 +41,7 @@ class AutoUpdater extends EventEmitter implements Electron.AutoUpdater {
       .catch(this.emitError.bind(this));
   }
 
-  emitError(error: any) {
+  emitError(error: string | Error) {
     if (typeof error === 'string') {
       error = new Error(error);
     }
diff --git a/app/config.ts b/app/config.ts
index ab4a3542..786c9340 100644
--- a/app/config.ts
+++ b/app/config.ts
@@ -7,7 +7,7 @@ import {cfgPath, cfgDir} from './config/paths';
 import {getColorMap} from './utils/colors';
 import {parsedConfig, configOptions} from '../lib/config';
 
-const watchers: any[] = [];
+const watchers: Function[] = [];
 let cfg: parsedConfig = {} as any;
 let _watcher: fs.FSWatcher;
 
diff --git a/app/notifications.ts b/app/notifications.ts
index fa59a8e4..ad7aaabd 100644
--- a/app/notifications.ts
+++ b/app/notifications.ts
@@ -7,7 +7,7 @@ const NEWS_URL = 'https://hyper-news.now.sh';
 
 export default function fetchNotifications(win: BrowserWindow) {
   const {rpc} = win;
-  const retry = (err?: any) => {
+  const retry = (err?: Error) => {
     setTimeout(() => fetchNotifications(win), ms('30m'));
     if (err) {
       console.error('Notification messages fetch error', err.stack);
diff --git a/app/notify.ts b/app/notify.ts
index c455fe55..0d1eaa52 100644
--- a/app/notify.ts
+++ b/app/notify.ts
@@ -1,7 +1,7 @@
 import {Notification} from 'electron';
 import {icon} from './config/paths';
 
-export default function notify(title: string, body = '', details: any = {}) {
+export default function notify(title: string, body = '', details: {error?: any} = {}) {
   console.log(`[Notification] ${title}: ${body}`);
   if (details.error) {
     console.error(details.error);
diff --git a/app/session.ts b/app/session.ts
index b376f48b..4af8a5b2 100644
--- a/app/session.ts
+++ b/app/session.ts
@@ -153,7 +153,7 @@ export default class Session extends EventEmitter {
       this.batcher?.write(chunk as any);
     });
 
-    this.batcher.on('flush', (data) => {
+    this.batcher.on('flush', (data: string) => {
       this.emit('data', data);
     });
 
diff --git a/app/ui/window.ts b/app/ui/window.ts
index 175ae748..df5107c0 100644
--- a/app/ui/window.ts
+++ b/app/ui/window.ts
@@ -149,7 +149,7 @@ export function newWindow(
       activeUid: options.activeUid
     });
 
-    session.on('data', (data: any) => {
+    session.on('data', (data: string) => {
       rpc.emit('session data', data);
     });
 
diff --git a/app/utils/cli-install.ts b/app/utils/cli-install.ts
index 88ca8241..e9f20ef4 100644
--- a/app/utils/cli-install.ts
+++ b/app/utils/cli-install.ts
@@ -86,7 +86,7 @@ const addBinToUserPath = () => {
   });
 };
 
-const logNotify = (withNotification: boolean, title: string, body: string, details?: any) => {
+const logNotify = (withNotification: boolean, title: string, body: string, details?: {error?: any}) => {
   console.log(title, body, details);
   withNotification && notify(title, body, details);
 };
diff --git a/cli/index.ts b/cli/index.ts
index 7fc03d53..95620066 100644
--- a/cli/index.ts
+++ b/cli/index.ts
@@ -1,6 +1,6 @@
 // This is a CLI tool, using console is OK
 /* eslint no-console: 0 */
-import {spawn, exec} from 'child_process';
+import {spawn, exec, SpawnOptions} from 'child_process';
 import {isAbsolute, resolve} from 'path';
 import {existsSync} from 'fs';
 import {version} from '../app/package.json';
@@ -42,7 +42,7 @@ args.command(
     commandPromise = api
       .install(pluginName)
       .then(() => console.log(chalk.green(`${pluginName} installed successfully!`)))
-      .catch((err: any) => console.error(chalk.red(err)));
+      .catch((err) => console.error(chalk.red(err)));
   },
   ['i']
 );
@@ -202,7 +202,7 @@ const main = (argv: string[]) => {
     env['ELECTRON_ENABLE_LOGGING'] = '1';
   }
 
-  const options: any = {
+  const options: SpawnOptions = {
     detached: true,
     env
   };
@@ -231,8 +231,8 @@ const main = (argv: string[]) => {
   const child = spawn(process.execPath, args_, options);
 
   if (flags.verbose) {
-    child.stdout.on('data', (data) => console.log(data.toString('utf8')));
-    child.stderr.on('data', (data) => console.error(data.toString('utf8')));
+    child.stdout?.on('data', (data) => console.log(data.toString('utf8')));
+    child.stderr?.on('data', (data) => console.error(data.toString('utf8')));
   }
   if (flags.verbose) {
     return new Promise((c) => child.once('exit', () => c(null)));
@@ -247,7 +247,7 @@ function eventuallyExit(code: number) {
 
 main(process.argv)
   .then(() => eventuallyExit(0))
-  .catch((err: any) => {
+  .catch((err) => {
     console.error(err.stack ? err.stack : err);
     eventuallyExit(1);
   });
diff --git a/lib/actions/sessions.ts b/lib/actions/sessions.ts
index 356cfe13..af77f765 100644
--- a/lib/actions/sessions.ts
+++ b/lib/actions/sessions.ts
@@ -50,7 +50,7 @@ export function requestSession() {
   };
 }
 
-export function addSessionData(uid: string, data: any) {
+export function addSessionData(uid: string, data: string) {
   return (dispatch: HyperDispatch) => {
     dispatch({
       type: SESSION_ADD_DATA,
@@ -161,7 +161,7 @@ export function closeSearch(uid?: string, keyEvent?: any) {
   };
 }
 
-export function sendSessionData(uid: string | null, data: any, escaped?: any) {
+export function sendSessionData(uid: string | null, data: any, escaped?: boolean | null) {
   return (dispatch: HyperDispatch, getState: () => HyperState) => {
     dispatch({
       type: SESSION_USER_DATA,
diff --git a/lib/actions/ui.ts b/lib/actions/ui.ts
index 9838ee7a..02e80366 100644
--- a/lib/actions/ui.ts
+++ b/lib/actions/ui.ts
@@ -112,16 +112,15 @@ export function windowGeometryUpdated(): HyperActions {
 
 // Find all sessions that are below the given
 // termGroup uid in the hierarchy:
-const findChildSessions = (termGroups: any, uid: string): string[] => {
+const findChildSessions = (termGroups: HyperState['termGroups']['termGroups'], uid: string): string[] => {
   const group = termGroups[uid];
   if (group.sessionUid) {
     return [uid];
   }
 
-  return group.children.reduce(
-    (total: string[], childUid: string) => total.concat(findChildSessions(termGroups, childUid)),
-    []
-  );
+  return group.children
+    .asMutable()
+    .reduce((total: string[], childUid: string) => total.concat(findChildSessions(termGroups, childUid)), []);
 };
 
 // Get the index of the next or previous group,
@@ -318,7 +317,7 @@ export function openSSH(url: string) {
   };
 }
 
-export function execCommand(command: string, fn: (...args: any[]) => void, e: any) {
+export function execCommand(command: string, fn: (e: any, dispatch: HyperDispatch) => void, e: any) {
   return (dispatch: HyperDispatch) =>
     dispatch({
       type: UI_COMMAND_EXEC,
diff --git a/lib/command-registry.ts b/lib/command-registry.ts
index 4c8e827d..27b6e513 100644
--- a/lib/command-registry.ts
+++ b/lib/command-registry.ts
@@ -3,7 +3,7 @@ import {HyperDispatch} from './hyper';
 import {closeSearch} from './actions/sessions';
 // TODO: Should be updates to new async API https://medium.com/@nornagon/electrons-remote-module-considered-harmful-70d69500f31
 
-const {getDecoratedKeymaps} = remote.require('./plugins');
+const {getDecoratedKeymaps} = remote.require('./plugins') as typeof import('../app/plugins');
 
 let commands: Record<string, (event: any, dispatch: HyperDispatch) => void> = {
   'editor:search-close': (e, dispatch) => {
@@ -16,7 +16,7 @@ export const getRegisteredKeys = () => {
 
   return Object.keys(keymaps).reduce((result: Record<string, string>, actionName) => {
     const commandKeys = keymaps[actionName];
-    commandKeys.forEach((shortcut: string) => {
+    commandKeys.forEach((shortcut) => {
       result[shortcut] = actionName;
     });
     return result;
diff --git a/lib/components/term-group.tsx b/lib/components/term-group.tsx
index 65d37b85..312c9a6a 100644
--- a/lib/components/term-group.tsx
+++ b/lib/components/term-group.tsx
@@ -12,13 +12,13 @@ const SplitPane = decorate(SplitPane_, 'SplitPane');
 // eslint-disable-next-line @typescript-eslint/class-name-casing
 class TermGroup_ extends React.PureComponent<TermGroupProps> {
   bound: WeakMap<(uid: string, ...args: any[]) => any, Record<string, (...args: any[]) => any>>;
-  term?: Term_;
+  term?: Term_ | null;
   constructor(props: TermGroupProps, context: any) {
     super(props, context);
     this.bound = new WeakMap();
   }
 
-  bind<T extends (uid: string, ...args: any) => any>(
+  bind<T extends (uid: string, ...args: any[]) => any>(
     fn: T,
     thisObj: any,
     uid: string
@@ -52,7 +52,7 @@ class TermGroup_ extends React.PureComponent<TermGroupProps> {
     );
   }
 
-  onTermRef = (uid: string, term: Term_) => {
+  onTermRef = (uid: string, term: Term_ | null) => {
     this.term = term;
     this.props.ref_(uid, term);
   };
diff --git a/lib/components/terms.tsx b/lib/components/terms.tsx
index 5ce8daf3..3f497613 100644
--- a/lib/components/terms.tsx
+++ b/lib/components/terms.tsx
@@ -3,7 +3,7 @@ import {decorate, getTermGroupProps} from '../utils/plugins';
 import {registerCommandHandlers} from '../command-registry';
 import TermGroup_ from './term-group';
 import StyleSheet_ from './style-sheet';
-import {TermsProps} from '../hyper';
+import {TermsProps, HyperDispatch} from '../hyper';
 import Term from './term';
 import {ObjectTypedKeys} from '../utils/object';
 
@@ -14,7 +14,7 @@ const isMac = /Mac/.test(navigator.userAgent);
 
 export default class Terms extends React.Component<TermsProps> {
   terms: Record<string, Term>;
-  registerCommands: (cmds: Record<string, (...args: any[]) => void>) => void;
+  registerCommands: (cmds: Record<string, (e: any, dispatch: HyperDispatch) => void>) => void;
   constructor(props: TermsProps, context: any) {
     super(props, context);
     this.terms = {};
@@ -29,7 +29,7 @@ export default class Terms extends React.Component<TermsProps> {
     );
   }
 
-  onRef = (uid: string, term: Term) => {
+  onRef = (uid: string, term: Term | null) => {
     if (term) {
       this.terms[uid] = term;
     }
diff --git a/lib/containers/hyper.tsx b/lib/containers/hyper.tsx
index 3b503e16..ecd4e9cd 100644
--- a/lib/containers/hyper.tsx
+++ b/lib/containers/hyper.tsx
@@ -10,12 +10,13 @@ import {HeaderContainer} from './header';
 import TermsContainer from './terms';
 import NotificationsContainer from './notifications';
 import {HyperState, HyperProps, HyperDispatch} from '../hyper';
+import Terms from '../components/terms';
 
 const isMac = /Mac/.test(navigator.userAgent);
 
 class Hyper extends React.PureComponent<HyperProps> {
   mousetrap!: MousetrapInstance;
-  terms: any;
+  terms!: Terms;
   constructor(props: HyperProps) {
     super(props);
   }
@@ -35,8 +36,8 @@ class Hyper extends React.PureComponent<HyperProps> {
     }
   }
 
-  handleFocusActive = (uid: string) => {
-    const term = this.terms.getTermByUid(uid);
+  handleFocusActive = (uid?: string) => {
+    const term = uid && this.terms.getTermByUid(uid);
     if (term) {
       term.focus();
     }
@@ -81,7 +82,7 @@ class Hyper extends React.PureComponent<HyperProps> {
     window.rpc.on('term selectAll', this.handleSelectAll);
   }
 
-  onTermsRef = (terms: any) => {
+  onTermsRef = (terms: Terms) => {
     this.terms = terms;
     window.focusActiveTerm = this.handleFocusActive;
   };
@@ -153,7 +154,7 @@ const mapStateToProps = (state: HyperState) => {
 
 const mapDispatchToProps = (dispatch: HyperDispatch) => {
   return {
-    execCommand: (command: string, fn: (...args: any[]) => void, e: any) => {
+    execCommand: (command: string, fn: (e: any, dispatch: HyperDispatch) => void, e: any) => {
       dispatch(uiActions.execCommand(command, fn, e));
     }
   };
diff --git a/lib/hyper.d.ts b/lib/hyper.d.ts
index a494b90f..d503354e 100644
--- a/lib/hyper.d.ts
+++ b/lib/hyper.d.ts
@@ -1,10 +1,11 @@
 import {Immutable} from 'seamless-immutable';
+import Client from './utils/rpc';
 
 declare global {
   interface Window {
     __rpcId: string;
-    rpc: any;
-    focusActiveTerm: any;
+    rpc: Client;
+    focusActiveTerm: (uid?: string) => void;
   }
 }
 
@@ -154,6 +155,7 @@ export type hyperPlugin = {
   mapNotificationsState: any;
   mapTermsState: any;
   middleware: Middleware;
+  onRendererUnload: any;
   onRendererWindow: any;
   reduceSessions: ISessionReducer;
   reduceTermGroups: ITermGroupReducer;
@@ -190,11 +192,12 @@ import configureStore from './store/configure-store';
 export type HyperThunkDispatch = ThunkDispatch<HyperState, undefined, HyperActions>;
 export type HyperDispatch = ReturnType<typeof configureStore>['dispatch'];
 
+import {ReactChild} from 'react';
 type extensionProps = Partial<{
-  customChildren: any;
-  customChildrenBefore: any;
+  customChildren: ReactChild | ReactChild[];
+  customChildrenBefore: ReactChild | ReactChild[];
   customCSS: string;
-  customInnerChildren: any;
+  customInnerChildren: ReactChild | ReactChild[];
 }>;
 
 import {HeaderConnectedProps} from './containers/header';
@@ -206,8 +209,9 @@ export type HyperProps = HyperConnectedProps & extensionProps;
 import {NotificationsConnectedProps} from './containers/notifications';
 export type NotificationsProps = NotificationsConnectedProps & extensionProps;
 
+import Terms from './components/terms';
 import {TermsConnectedProps} from './containers/terms';
-export type TermsProps = TermsConnectedProps & extensionProps & {ref_: any};
+export type TermsProps = TermsConnectedProps & extensionProps & {ref_: (terms: Terms | null) => void};
 
 export type StyleSheetProps = {
   backgroundColor: string;
@@ -270,7 +274,7 @@ export type TermGroupOwnProps = {
   cursorAccentColor?: string;
   fontSmoothing?: string;
   parentProps: TermsProps;
-  ref_: (uid: string, term: Term) => void;
+  ref_: (uid: string, term: Term | null) => void;
   termGroup: Immutable<ITermGroup>;
   terms: Record<string, Term | null>;
 } & Pick<
@@ -354,7 +358,7 @@ export type TermProps = {
   onActive: () => void;
   onContextMenu: (selection: any) => void;
   onCursorMove?: (cursorFrame: {x: number; y: number; width: number; height: number; col: number; row: number}) => void;
-  onData: (data: any) => void;
+  onData: (data: string) => void;
   onResize: (cols: number, rows: number) => void;
   onTitle: (title: string) => void;
   padding: string;
@@ -371,6 +375,7 @@ export type TermProps = {
   url: string | null;
   webGLRenderer: boolean;
   webLinksActivationKey: string;
-} & extensionProps & {ref_?: any};
+  ref_: (uid: string, term: Term | null) => void;
+} & extensionProps;
 
 export type Assignable<T, U> = {[k in keyof U]: k extends keyof T ? T[k] : U[k]} & Partial<T>;
diff --git a/lib/index.tsx b/lib/index.tsx
index a1921fd0..b1f2c3ce 100644
--- a/lib/index.tsx
+++ b/lib/index.tsx
@@ -76,7 +76,7 @@ rpc.on('session add', (data) => {
   store_.dispatch(sessionActions.addSession(data));
 });
 
-rpc.on('session data', (d) => {
+rpc.on('session data', (d: string) => {
   // the uid is a uuid v4 so it's 36 chars long
   const uid = d.slice(0, 36);
   const data = d.slice(36);
diff --git a/lib/reducers/term-groups.ts b/lib/reducers/term-groups.ts
index 7e8955ce..e4e24169 100644
--- a/lib/reducers/term-groups.ts
+++ b/lib/reducers/term-groups.ts
@@ -46,7 +46,7 @@ const setActiveGroup = (state: ImmutableType<ITermState>, action: {uid: string})
 };
 
 // Reduce existing sizes to fit a new split:
-const insertRebalance = (oldSizes: ImmutableType<number[]>, index: any) => {
+const insertRebalance = (oldSizes: ImmutableType<number[]>, index: number) => {
   const newSize = 1 / (oldSizes.length + 1);
   // We spread out how much each pane should be reduced
   // with based on their existing size:
@@ -167,7 +167,7 @@ const removeGroup = (state: ImmutableType<ITermState>, uid: string) => {
   // it's safe to remove the group.
   if (group.parentUid && state.termGroups[group.parentUid]) {
     const parent = state.termGroups[group.parentUid];
-    const newChildren = parent.children.filter((childUid: any) => childUid !== uid);
+    const newChildren = parent.children.filter((childUid) => childUid !== uid);
     if (newChildren.length === 1) {
       // Since we only have one child left,
       // we can merge the parent and child into one group:
@@ -188,7 +188,7 @@ const removeGroup = (state: ImmutableType<ITermState>, uid: string) => {
     .set('activeSessions', state.activeSessions.without(uid));
 };
 
-const resizeGroup = (state: ImmutableType<ITermState>, uid: any, sizes: number[]) => {
+const resizeGroup = (state: ImmutableType<ITermState>, uid: string, sizes: number[]) => {
   // Make sure none of the sizes fall below MIN_SIZE:
   if (sizes.find((size) => size < MIN_SIZE)) {
     return state;
diff --git a/lib/utils/notify.ts b/lib/utils/notify.ts
index 46855226..bbb246b9 100644
--- a/lib/utils/notify.ts
+++ b/lib/utils/notify.ts
@@ -1,5 +1,5 @@
 /* eslint no-new:0 */
-export default function notify(title: string, body: string, details: Record<string, any> = {}) {
+export default function notify(title: string, body: string, details: {error?: any} = {}) {
   console.log(`[Notification] ${title}: ${body}`);
   if (details.error) {
     console.error(details.error);