The synthesis and spectrokinetic properties of photochromic spiropyrans in solution are reported. The most important results obtained during the last two decades, including the synthetic access to azaheterocyclic and non-azaheterocyclic spiropyrans are described, as each series confers its own particularities to the photocoloration. The influence of the structure (skeleton, heteroatoms, substituents) on the stability of the photomerocyanines is discussed in terms of electronic (correlation of Hammett type) and steric effects. The role of structural parameters and of solvent effects on the electronic distribution of the colored form is also emphasized.