PATTERNS AND MECHANISMS: Mosaicism as a Biological Concept: -- History -- Mosaicism in Plants, Animals, Humans -- Mosaicism Versus Chimerism -- The Mechanisms of Mosaicism -- Genomic Mosaicism of Autosomes -- Epigenetic Mosaicism of autosomes -- Genomic Mosaicism of X Chromosomes -- Epigenetic Mosaicism of X Chromosomes -- The patterns of Mosaicism -- Lines of Blaschko -- Checkerboard Pattern -- Phylloid Pattern -- Patchy Pattern Without Midline Separation -- Lateralization -- Other Patterns, so far Unclassifiable -- MOSAIC SKIN DISORDERS: Nevi -- Melanocytic Nevi -- Other Forms of Pigmentary Mosaicism -- Epidermal Nevi -- Vascular Nevi -- Connective Tissue Nevi -- Nevoid Skin Disorders -- Lyonization (Functional X-Chromosome Mosaicism) in X-Linked Skin Disorders -- Autosomal Non-Nevi -- Neoplastic Skin Lesions -- Benign Tumors -- Malignant Tumors -- CONCLUSION.