Do not assume that your project belongs in the same category that it had in the previous competition.
Every science fair uses its own unique categories and their definitions. Read through all of the category definitions below to find the one that best describes what you studied in your project. For convenience the categories have been organized broadly into groups, but do not limit your category search only to one group. For example, studies of the effects of a chemical on a plant might, depending upon the details, be classified either as Plant Biology (in the Life Science group) or Toxicology (in the Environmental group). Read all of the definitions of possibly relevant categories.
Further, recognize that on your application you will not select the category for your project.
Instead, you will identify the category that you believe to be most appropriate. However, a committee of experienced judges will read your Project Summary and advise the Directors of Judging as to the correct placement. Those recommendations will be based solely on the definitions below and not on those from any other science fair. In the vast majority of cases the recommended category will be the same as that identified by the student. If it is not, and you think your category placement is incorrect, in your appeal to the Directors of Judging you will need to justify any requested category according to the definitions below.

Click here to expand all category definitions

Life Science Categories

05. Biochemistry/ Molecular Biology
12. Mammalian Biology
15. Microbiology (General)
16. Microbiology (Medical)
18. Plant Biology
22. Zoology

Physical Science Categories

01. Aerodynamics/ Hydrodynamics
02. Alternative Energy
03. Applied Mechanics & Structures
06. Chemistry
10. Electronics & Electromagnetics
13. Materials Science
17. Physics & Astronomy

Mathematical/ Computational Categories

08. Computational Systems & Analysis
14. Mathematical Sciences

Environmental Categories

09. Earth & Environmental Sciences
11. Environmental Engineering
21. Toxicology

Behavioral/ Cognitive Categories

04. Behavioral & Social Sciences
07. Cognitive Science

Product Testing Categories

19. Product Science (Biological)
20. Product Science (Physical)
California Science & Engineering Fair / 2020 / Category Definitions /