The overlap integral is a measure of the extent of overlap of an orbital of an atom with the orbital of another atom .

The diagram above depicts the graphs of and for points along the internuclear axis of two orbitals. With regard to the two graphs of , is the continuous sum of the product of the wavefunctions and at each .

if the wavefunctions overlap and if the wavefunctions do not overlap. This implies that if , bonding does not occur between the atoms because the orbitals of the two atoms are too far apart. Therefore, not only provides a quantitative measure of the extent of overlap of an orbital of an atom with the orbital of another atom , but an indication of whether bonding is possible.

Group theory is often employed to determine if the overlap integral between two wavefunctions is necessarily zero without having to compute the integral algebraically.