Kolban's Book on ESP32 by Neil Kolban is a large free guide to programming and using the Espressif ESP32 Wi-Fi and Bluetooth microcontroller. It introduces the ESP32 specification, variants and modules such as ESP-WROOM-32, DevKitC and WROVER-KIT, and explains connecting the board, USB to UART converters, power and test equipment. The main part covers the ESP-IDF development framework: the build system, menu configuration, components, error handling, memory, FreeRTOS tasks, GPIO, timers, Wi-Fi, TCP/IP sockets, HTTP, Bluetooth, I2C, SPI, flash storage and many peripherals, with Arduino and JavaScript options. Full of code samples, it suits makers and embedded developers.