Agile software development (ASD) has emerged as a practice-led initiative which offers great promise in improving software productivity. However some confusion exists as to its relationship with Lean Software Development (LSD). Some treat LSD as more or less synonymous with ASD whereas others view LSD as a different concept. The definition and positioning of LSD relative to ASD is important as it gets to the heart of software development as craft versus science debate. The purpose of this paper is to identify core LSD values that 'define' LSD much as the agile manifesto values unified and defined so-called "lightweight methods" for ASD. We posit that LSD is more management philosophy than method and illuminate this through a genealogical analysis of the origins of LSD. We identify principles from various sources on the application of lean thinking in different domains. Synthesizing these principles we derive a candidate set of lean values that characterise LSD. Although immediately valuable to practitioners seeking to apply lean values in agile projects, future research will use this value-set to assess elements of "lean thinking" in the practices and principles of various agile methods so as to facilitate optimal applicability of these methods in a lean context.