 This article focuses on the subject matter of biology: life. The first half of this article will focus on attempts to characterize life by both philosophers and scientists. The first section will describe alternative accounts of definitions, its two subsections will cover historical and contemporary definitions, and section 2 covers the recent countertrend in skepticism toward definitions of life. Because the various stakeholders have different goals, the second half will focus on those goals. Sections 3, 4, and 5 cover topics that some believe require a definition of life: artificial and synthetic life, the origin(s) of life, and the search for life in the Universe. Section 6 covers entities that are much larger or smaller than organisms, while section 7 covers the role life takes in the context of society, especially with respect to questions raised by new technology.