The process by which a protein finds its unique three-dimensional structure. For many years one of the main difficulties in the theory of protein folding was the Levinthal paradox, which raises the question of how a protein finds its unique structure so rapidly. In the 1980s and 1990s a solution was suggested by the energy landscape concept; the energy landscape of proteins is described as having a ‘funnel’ shape, with the correct structure at the bottom of the funnel. Misfolding of proteins can result in conditions such as Alzheimer’s disease.