The shape of CdSe and other semiconductor nanocrystals is controlled, producing dots, rods, rice-shaped particles, tetrapods, or other elongated shapes. Monomer concentration in the growth solution is the determining factor in shape-control and shape-evolution. The elongated shapes could be transformed into more spherical shapes if the monomer concentration in the solution was lowered to a certain level, and spherically shaped nanocrystals could grow to elongated shapes by simply increasing the monomer concentration. The precursors are stable, inexpensive, and relatively non-toxic, and therefore good choices for the growth of nearly monodisperse and shape-controlled nanocrystals.