The chapter delves into the specific kind of understanding aimed at in medicine, starting from the Understanding Thesis. Drawing on recent work by Broadbent (2019), debates in the epistemology of understanding (Kvanvig 2009; Grimm 2012; Khalifa 2017), and scholarship on the aims of inquiry, the chapter unpacks what it means to understand something, differentiating types of understanding, and using the history of scurvy to explore understanding a disease in medicine. The hypothesis is that biomedical understanding of a disease requires grasping a mechanistic explanation of the disease. This understanding of causal and constitutive relationships draws on an influential account of causation (Woodward 2003; 2010; 2015) and work on mechanistic explanations in biological sciences and neuroscience (Thagard 2003; 2005; Craver 2007; Nervi 2010; Kaplan and Craver 2011; Darrason 2018). However, it argues that biomedical understanding is necessary but not sufficient for clinical understanding, which combines biomedical understanding of a disease with personal understanding of an illness. This chapter revisits the distinction between "understanding" and "explanation" from debates in the field.