In science, a process that is not reversible is called irreversible. This concept arises most frequently in thermodynamics.

Reversibility can refer to:

• Time reversibility, a property of some mathematical or physical processes and systems for which time-reversed dynamics are well defined

• Reversible diffusion, an example of a reversible stochastic process

• Reversible process (thermodynamics), a process or cycle such that the net change at each stage in the combined entropy of the system and its surroundings is zero
• Reversible reaction, a chemical reaction for which the position of the chemical equilibrium is very sensitive to the imposed physical conditions; so the reaction can be made to run either forwards or in reverse by changing those conditions
• Reversible computing, logical reversibility of a computation - a computational step for which a well-defined inverse exists
• Reversible error, a legal mistake invalidating a trial
• Reversible garment, a garment that can be worn two ways
• Piaget's theory of cognitive development, in which mental reversibility is part of the concrete operational stage, the understanding that numbers and objects can change and then return to their original state
• Tesla principle, now known as a reversible process in engineering, a process of a system such that a net reverse in operation will accomplish the converse of the original function