Many studies have been conducted on deformations in wood and pulp fibres, and a large number of terms (e.g, dislocations, microcompressions, slip planes, nodes, misaligned zones, crimps, kinks) have been used to describe these structures in the literature. The true structure of deformations however. remains unclear because most observations are based on light microscopical studies. In the present work, the nature and structure of fibre deformations are discussed from an ultrastructural perspective in the light of old and new observations. In several cases, previous studies appear to have described similar types of deformations but with varying extent resulting in confusion regarding definition. Evidence for the occurrence of deformations in wood cells of living trees is also reviewed.