The marginal rate of technical substitution (MRTS) is an economic theory that illustrates the rate at which one factor must decrease so that the same level of productivity can be maintained when another factor is increased.

The MRTS reflects the give-and-take between factors, such as capital and labor, that allow a firm to maintain a constant output. MRTS differs from the marginal rate of substitution (MRS) because MRTS is focused on producer equilibrium and MRS is focused on consumer equilibrium.