What are the different power management modes in microcontrollers?

Power modes trade-off power consumption vs functionality: Active/Run (full operation, highest power), Idle/Sleep (CPU stopped, peripherals active, fast wake), Standby/Stop (most peripherals stopped, RAM retained, medium wake time), and Deep Sleep/Shutdown (minimal power, RAM may be lost, slow wake). Wake sources include external interrupts, RTC, and watchdog. Power optimization strategies: sleep when idle, disable unused peripherals, reduce clock speed, and use low-power peripherals. ARM Cortex-M uses WFI/WFE instructions to enter sleep.