The fluid portion of an adult human’s total body mass is 60% in males and 55% in females. This fluid is distributed into two major compartments: intracellular fluid (2/3) and extracellular fluid (1/3). In this chapter, we primarily focus on extracellular fluids, which include blood plasma, interstitial fluid, and lymph in the lymphatic system. We begin with an overview of all major fluid compartments, distinguishing between intracellular fluids, extracellular fluids, and the subdivisions of the latter. Next, we examine the interstitial fluid (ISF) and its direct connection to the vascular and lymphatic systems. A section is then dedicated entirely to the lymphatic system and its anatomical connections with other systems. The chapter concludes with a summary and suggestions for further reading.