Microcontrollers are small computers contained on a single chip that are used for embedded applications. When selecting a microcontroller, factors to consider include the number of input/output pins needed, required interfaces like PWM, memory requirements for code and data, number of interrupts, required processing speed, cost and power constraints, available analog components, communication protocols, product family and available development tools, timers needed, and environmental conditions. Microcontrollers are commonly used in automotive, medical, consumer, and industrial devices to control automated processes.