- Cl (Chlorine)
- Cl., Clico. (Clericus, Clerico ("Cleric"))
- CLA (Clutterers Anonymous)
- Cla. (Clausula ("Clause"))
- CLACS (Center for Latin American and Caribbean Studies)
- CLAD (Culture, Language, and Academic Development)
- CLAGS (Center for Lesbian and Gay Studies)
- CLAI (Christian Legal Association of India)
- CLAIM (Chicago Legal Advocacy for Incarcerated Mothers)
- CLAIRE (Cyber Linguistic Artificial Intelligence Research Engine)
- CLAIT (Computer Literacy And Information Technology)
- CLAM (Child Language Ability Measures)
- CLAMS (Clear lane marking system (US))
- CLAN (Cute Little Awesome Newborn)
- CLAP (Carbohydrates, Lipid, Nucleic Acid, Protein)
- CLAPC/CLIPC (Contact lens associated/induced papillary conjunctivitis)
- CLAPS (Culture, Language, Arts, Programs, Services)
- CLAR (Communications Loading Analysis Report)
- CLARE (Contact lens associated red eye)
- CLAS (California Learning Assessment System)