Undergraduate and Graduate level course numbering is as such:

001-099Pre-college level courses (not applicable to a degree).
100-299Lower-division courses (when applicable, 100-199 freshmen; 200-299 sophomores) undergraduate credit only.
300-499Upper-division courses (when applicable, 300-399 junior; 400-499 senior) undergraduate credit only.
500-599Advanced upper-division courses in which graduate students may enroll and receive graduate credit. (It is assumed that graduate students will perform more requirements and be graded more strictly than undergraduates in these courses.)
600-799Graduate courses (master's and doctoral level).
800-899Graduate courses (limited to doctoral candidates).
900-999Post-doctoral (or post-terminal) degree courses only.