What are the differences between undermount sinks and top mount sinks?

Undermount sinks are installed beneath the countertop for a seamless look, while top mount sinks are placed on top of the countertop. Undermount sinks are easier to clean and provide a sleek appearance, but require professional installation. Top mount sinks are simpler to install and can be easily replaced, but may have a more visible rim and be harder to clean around.