The double-quartet theory of Linnett is shown to account for a wide variety of typical organic structural phenomena. The concept of L strain, a unique corollary of the Linnett theory, is discussed and put on a semiquantitative basis. Examples of problems in geometry, stabilization, hyperconjugation, and configurational inversion are provided from among the classes alkanes, alkenes, alkynes, amines, carbanions, carbonium ions, radicals, and carbenes, and certain predictions are made. © 1969, American Chemical Society. All rights reserved.