diff --git a/web3.js/README.md b/web3.js/README.md
index 328524f947..67d42756d5 100644
--- a/web3.js/README.md
+++ b/web3.js/README.md
@@ -65,6 +65,18 @@ console.log(solanaWeb3);
 console.log(solanaWeb3);
 ```
 
+## Flow
+
+A Flow library definition file is provided at
+[module.flow.js](https://github.com/solana-labs/solana-web3.js/tree/master/module.flow.js).
+Add the following line under the [libs] section of your project's .flowconfig to
+activate it:
+```ini
+[libs]
+node_modules/@solana/web3.js/module.flow.js
+```
+
+
 ## Examples
 See the [examples/](https://github.com/solana-labs/solana-web3.js/tree/master/examples) directory for small snippets.
 
diff --git a/web3.js/module.flow.js b/web3.js/module.flow.js
new file mode 100644
index 0000000000..2221cd6b1a
--- /dev/null
+++ b/web3.js/module.flow.js
@@ -0,0 +1,89 @@
+/**
+ * Flow Library definition for @solana/web3.js
+ *
+ * This file is manually generated from the contents of src/
+ *
+ * Usage: add the following line under the [libs] section of your project's
+ * .flowconfig:
+ * [libs]
+ * node_modules/@solana/web3.js/module.flow.js
+ *
+ */
+
+declare module '@solana/web3.js' {
+  declare type PublicKey = string;
+
+  // === src/account.js ===
+  declare export class Account {
+    constructor(secretKey: ?Buffer): Account;
+    publicKey: PublicKey;
+    secretKey: PublicKey;
+  }
+
+  // === src/budget-program.js ===
+  /* TODO */
+
+  // === src/connection.js ===
+  declare type AccountInfo = {
+    tokens: number,
+    programId: PublicKey,
+    userdata: Buffer | null,
+  }
+
+  declare type SignatureStatus = 'Confirmed' | 'SignatureNotFound' | 'ProgramRuntimeError' | 'GenericFailure';
+
+  declare export class Connection {
+    constructor(endpoint: string): Connection;
+    getBalance(publicKey: PublicKey): Promise<number>;
+    getAccountInfo(publicKey: PublicKey): Promise<AccountInfo>;
+    confirmTransaction(signature: TransactionSignature): Promise<boolean>;
+    getSignatureStatus(signature: TransactionSignature): Promise<SignatureStatus>;
+    getTransactionCount(): Promise<number>;
+    getLastId(): Promise<TransactionId>;
+    getFinality(): Promise<number>;
+    requestAirdrop(to: PublicKey, amount: number): Promise<TransactionSignature>;
+    sendTransaction(from: Account, transaction: Transaction): Promise<TransactionSignature>;
+  }
+
+  // === src/system-program.js ===
+  declare export class SystemProgram {
+    static programId: PublicKey;
+
+    static createAccount(
+      from: PublicKey,
+      newAccount: PublicKey,
+      tokens: number,
+      space: number,
+      programId: PublicKey
+    ): Transaction;
+    static move(from: PublicKey, to: PublicKey, amount: number): Transaction;
+    static assign(from: PublicKey, programId: PublicKey): Transaction;
+  }
+
+  // === src/transaction.js ===
+  declare type TransactionSignature = string;
+  declare type TransactionId = string;
+
+  declare type TransactionCtorFields = {|
+    signature?: Buffer;
+    keys?: Array<PublicKey>;
+    programId?: PublicKey;
+    fee?: number;
+    userdata?: Buffer;
+  |};
+
+
+  declare export class Transaction {
+    signature: ?Buffer;
+    keys: Array<PublicKey>;
+    programId: ?PublicKey;
+    lastId: ?TransactionId;
+    fee: number;
+    userdata: Buffer;
+
+    constructor(opts?: TransactionCtorFields): Transaction;
+    sign(from: Account): void;
+    serialize(): Buffer;
+    static serializePublicKey(key: PublicKey): Buffer;
+  }
+}