In this chapter, we will introduce key topics on fundamentals of ultrasound imaging to provide the basis for understanding how this powerful imaging modality works without going into any sophisticated theories. The primary focus will be on commonly used terminologies and concepts. The chapter begins with a concise overview of the physics characterizing ultrasound waves, followed by a comprehensive introduction of ultrasound transducers. This includes the internal structure of the transducer and their characteristics along with types of transducers frequently employed in research and/or clinics as well as transducer selection criteria. Then, we will move forward by introducing fundamentals of ultrasound image formation, important characteristics of ultrasound B-mode images as well as presenting some advanced ultrasound imaging modes. We will conclude the chapter by discussing important ultrasound imaging artifacts and essential safety considerations.