Although Knowledge Management (KM) has been acknowledged as the most important resource and capability of an organisation, many academics' standpoints argue upon knowledge distinct characteristics. This paper is a critical review of KM literature and attempts to clarify different knowledge perspectives and offer a holistic picture of one of the most controversial issues to management science. We, first, build our critique on knowledge theory, explaining what knowledge is. Regarding different knowledge perspectives, such as Nonaka's, Tsoukas' and Blackler's, we attempt to clarify how knowledge interacts and is affected by their unique views. Second, we review KM theory according to the analysed knowledge perspectives. Finally, we categorise KM theory to three approaches: the cognitive, the community and the network approach, and we consider their impact to organisations.