The present review represents an attempt towards a unified picture of the direct transition from the isotropic to smectic-A phase. The isotropic to smectic-A phase transition is described in detail, including structure and nature revealed by experiments, molecular models and Landau-de Gennes theory. The wide variety of phenomena including effects of nonmesogenic impurities and electric field, hydrodynamics, fluctuations, and elastic theory of liquid crystalline elastomers is discussed. A brief review on the general information about the isotropic to lamellar phase transition in lyotropic liquid crystals has been given. The various predictions are compared with the available experimental results. Open questions and possible approaches to finding answers are discussed.