Piezoelectric materials are commonly used as sensors and actuators, for energy harvesting and vibration control in many industrial and every-day devices. They have established themselves as well in the medical device market as core components in e.g. ultrasound applications and for surgical tools. For in vivo applications, however, piezoelectric materials have not made the jump into clinical usage yet, even though they could enable localized pressure sensing, energy harvesting from muscle motion or stimulation of tissue re-generation after surgery. The main challenge here is that they have to be biocompatible. This is a concept that goes way beyond simple chemical toxicity, but covers all aspects that influence the safe performance of a material at the implant site under the complex conditions that the body imposes. In this tutorial, we will take an in-depth look at the applicability and biocompatibility of piezoelectric materials for in vivo biomedical applications. We will investigate the boundary conditions that the body imposes on implant materials in different applications and how these might impact the functionality and stability of piezoelectric implants. And vice versa we will look into the influence of material properties, such as surface topography, chemical composition and mechanical properties, on the living system. Based on this, we will discuss future application areas for this versatile class of materials in the biomedical realm.