**Abstract**

In recent times, terms such as 'interfascial plane block' and 'fascial plane block' have become common in describing regional anaesthesia blocks such as transversus abdominis plane (TAP), serratus anterior plane (SAP) and erector spinae plane (ESP). In fact, none of these names accurately describes the applied anatomy involved in each named technique, as the acronym is only one part of the anatomic jigsaw puzzle. The correct term is 'tissue plane block', which derives from surgical terminology. The tissue plane is not new to regional anaesthesia, as it has been the endpoint of 'loss of resistance' and 'pop' techniques for many decades. However, the game-changer is that now we can see the tissue plane courtesy of ultrasound. The purpose of this chapter is to review the history of the tissue plane in relation to its use in regional anaesthesia, and to see how ultrasound has further advanced the regional anaesthesiologist's options in this regard. The chapter will also review how an understanding of tissue dynamics can further enhance our clinical results by manipulating the characteristics of the tissue plane.

**Keywords:** tissue plane, ultrasound-guided regional anaesthesia, applied anatomy, TAP block, ESP block, SAP block, rectus sheath block, tissue plane dynamics, dye studies, injectate, hydrodissection, nerve block
