What is the difference between synchronous and asynchronous counters?

In asynchronous (ripple) counters, each flip-flop is clocked by the output of the previous stage, causing propagation delay that accumulates. In synchronous counters, all flip-flops are clocked simultaneously by the same clock signal, with combinational logic determining next states. Synchronous counters are faster (no ripple delay), easier to design for complex sequences, and have predictable timing. Asynchronous counters are simpler but limited to lower frequencies due to accumulated delay.