In situ transmission electron microscopy (TEM) is a really rich topic and is still viewed as a non-traditional microscopy, as it involves a lot of different processes. This chapter gives some explanations about in situ TEM mostly dedicated to the study of devices. It lists the various forms of in situ TEM techniques regarding their physical meaning conjugated to their experimental requirements. The forms of in situ TEM techniques include temperature control and electron irradiation, electromagnetic field applications, mechanical traction or compression, chemistry, light interaction, and current injection constraint. The chapter reviews commercial and homemade sample holder designs such as multi-contact holders and movable contact holders. The chapter finally describes some of the most common tools that can be used to easily design a TEM sample that can be fitted within the sample holders. The tools discussed are focused ion beam and TEM windows.