The emergence of quantum mechanics in 1920s opened an intense discussion, which continues to these days, about its interpretation. This article aims to contribute to this discussion. First, a definition of ontic (really existing) and epistemic (pertaining to knowledge) states of a quantum system is proposed. Based on these definitions, the key concepts and postulates of quantum mechanics such as quantum state collapse, measurements and system properties, statistical inference, and key properties of quantum probability calculus are discussed. An alternative interpretation of degenerate ontic states is presented. The proposed ontological and epistemological framework for quantum mechanics is applied to explain Schrödinger’s cat paradox, to redefine quantum entanglement, to illustrate quantum entanglement based on the Bohm’s variant of the Einstein-Podolsky-Rosen (EPR) paradox, and to substantiate the principle of local causality. This framework is further compared with the quantum histories approach, quantum information approach, and spontaneous collapse approach.