This chapter provides an overview of the atmospheric boundary layer. It begins with definitions and descriptions of the vertical structures of the atmospheric boundary layer (Sect. 1.1), followed by discussions on mean winds, turbulence, and waves (Sect. 1.2). A brief overview of the wind spectrum is then presented (Sect. 1.3). This chapter focuses on the meteorological basics, which are then expanded in Chap.  2 on theoretical aspects and Chap.  3 on experimental and numerical methods.