Hardening is the process by which something becomes harder or is made harder.
Hardening may refer to:
- Hardening (metallurgy), a process used to increase the hardness of a metal
- Hardening (botany) or cold hardening, a process in which a plant undergoes physiological changes to mitigate damage from cold temperatures
- Hardening (computing), the process of securing a system against attack
- Target hardening, strengthening of the security of a building or installation to protect it from attack
- Sclerotization, a biochemical process forming cuticle in arthropods