async and await — C# Reference, Syntax & Examples

Read the syntax

An async method commonly returns Task or Task<T>; await suspends that method until an awaitable operation completes. It does not automatically create a new thread.

Task.Delay represents an asynchronous wait, unlike Thread.Sleep, which blocks the calling thread. Awaiting operations in sequence preserves their order; start independent tasks first when concurrency is needed.

Syntax

async Task MethodName() {\n  await SomeAsyncOperation();\n}

Examples

A Basic Async Method

Marking a method async and awaiting a delay.

async Task GreetAfterDelayAsync()
{
    Console.WriteLine("Starting...");
    await Task.Delay(1000);  // pauses here without blocking the thread
    Console.WriteLine("One second later!");
}

await GreetAfterDelayAsync();

Marking a method async and awaiting a delay.
An async method commonly returns Task or Task<T>; await suspends that method until an awaitable operation completes. It does not automatically create a new thread.
The method prints Starting..., awaits an approximately one-second delay, then prints One second later!. The caller awaits the method before continuing.

Async Methods That Return a Value

async Task<T> is the async equivalent of a method that returns T.

async Task<int> GetNumberAsync()
{
    await Task.Delay(500);
    return 42;
}

int result = await GetNumberAsync();
Console.WriteLine(result);  // 42

async Task<T> is the async equivalent of a method that returns T.
An async method commonly returns Task or Task<T>; await suspends that method until an awaitable operation completes. It does not automatically create a new thread.
Task<int> carries a future int result. After the delay, return 42 completes the task; the caller’s await obtains and prints 42.

Why Async Matters: Not Blocking the Thread

Comparing a blocking synchronous wait to a non-blocking async one.

// Synchronous: blocks the calling thread entirely for 2 seconds
void BlockingWait()
{
    Thread.Sleep(2000);
    Console.WriteLine("Done (blocked the thread the whole time)");
}

// Asynchronous: frees the thread to do other work while waiting
async Task NonBlockingWaitAsync()
{
    await Task.Delay(2000);
    Console.WriteLine("Done (thread was free to do other work)");
}

await NonBlockingWaitAsync();

Comparing a blocking synchronous wait to a non-blocking async one.
An async method commonly returns Task or Task<T>; await suspends that method until an awaitable operation completes. It does not automatically create a new thread.
The example calls only NonBlockingWaitAsync; BlockingWait is declared for comparison but never invoked. After a delay it prints the nonblocking completion message.

Awaiting Multiple Steps in Sequence

await pauses at each step, but the code still reads top-to-bottom like synchronous code.

async Task<string> FetchDataAsync()
{
    Console.WriteLine("Step 1: connecting...");
    await Task.Delay(300);

    Console.WriteLine("Step 2: downloading...");
    await Task.Delay(300);

    return "data loaded";
}

string data = await FetchDataAsync();
Console.WriteLine(data);

await pauses at each step, but the code still reads top-to-bottom like synchronous code.
An async method commonly returns Task or Task<T>; await suspends that method until an awaitable operation completes. It does not automatically create a new thread.
Each delay is awaited before the next step starts. The output shows connecting, downloading and data loaded in that order.

Best practices

Name async methods with an "Async" suffix (GetDataAsync, not GetData) - a strong, widely followed C# convention
Use async Task instead of async void for any method except top-level event handlers - async void methods cannot be awaited and make error handling much harder
Await asynchronous operations all the way up the call chain rather than blocking on them with .Result or .Wait(), which can cause deadlocks in some contexts (like UI apps)
Reserve async/await for genuinely I/O-bound work (network, disk, database) - it does not speed up CPU-bound computation on its own

Runtime & versions

.NET runtime. Feature availability depends on the language and runtime version used by your project; consult the official reference below.

C# language reference

Specifications & further reading

C# language reference