Due to the close coupling of earphones to the ears and the acoustic transmission paths involved, headphone measurements are complicated. This paper will discuss these challenges, types of headphones, measurement standards, headphone acoustics, acoustic test fixtures required for measuring headphones, and the practical aspects of headphone measurements. We’ll also focus on objective measurements, providing an overview of the key electroacoustic measurements used to characterize the audio quality of headphones and earphones intended for listening to music and other full-band audio program material.