This chapter explores the nature of lentic periphyton. First, the lentic habitat and flora will be examined with the following questions in mind: Where are the periphyton microhabitats and what is their nature? Is there a distinct lentic subset of periphyton? Next, an overview of influential parameters affecting periphyton and particularly lentic periphyton will be presented, followed by a detailed examination of important biotic and abiotic factors that potentially regulate periphyton structure and function in lentic ecosystems.