Channels are a typed conduit through which you can send and receive values:

ch <- v    // Send v to channel ch.
v := <-ch  // Receive from ch, and
           // assign value to v.

(The data flows in the direction of the arrow.)

Like maps and slices, channels must be created before use:

ch := make(chan int)

By default, sends and receives block until the other side is ready. This allows goroutines to synchronize without explicit locks or condition variables.

Here's an example that sums the numbers in a slice, distributing the work between two goroutines:

func sum(s []int, c chan int) {
	sum := 0
	for _, v := range s {
		sum += v
	}
	c <- sum // send sum to c
}

func main() {
	s := []int{7, 2, 8, -9, 4, 0}

	c := make(chan int)
	go sum(s[:len(s)/2], c)
	go sum(s[len(s)/2:], c)
	x, y := <-c, <-c // receive from c

	fmt.Println(x, y, x+y)
}

buffers

Channels can be buffered. Provide the buffer length as the second argument to make to initialize a buffered channel:
ch := make(chan int, 100)

Sends to a buffered channel block only when the buffer is full. Receives block when the buffer is empty.

range and close

A sender can close a channel to indicate that no more values will be sent. Receivers can test whether a channel has been closed by assigning a second parameter to the receive expression:
v, ok := <-ch

ok is false if there are no more values to receive and the channel is closed.

The loop for i := range c receives values from the channel repeatedly until it is closed.

NOTE: Only the sender should close a channel, never the receiver. Sending on a closed channel will cause a panic.

pipelines

Pipelines are often constructed by stringing together simple functions that have an incoming and outgoing channel and modify data being passed through them. The start and ending of a pipeline are of course different, having only an output or input respectively.