A - Income Tax (Parts 1-19)
B - Estate and Gift Taxes (Parts 20-26)
C - Employment Taxes (Parts 30-39)
D - Miscellaneous Excise Taxes (Parts 40-169)
E - Reserved (Parts 170-299)
F - Procedure and Administration (Parts 300-499)
G - Tax Conventions (Parts 500-521)
H - Internal Revenue Practice (Parts 600-801)