The most important classes of illegal contracts are the following:

Agreements in restraint of trade.8

Sunday laws.9

Wagers.10

Usury.11

Ultra vires agreements.12

Agreements which tend to prejudice a nation in relation with other nations.13

Agreements which tend to injure the public service.14

Agreements which tend to increase litigation.15

Agreements which tend to obstruct justice.16

Agreements which involve immorality.17

Agreements in restraint of marriage.18

Agreements, lawful in themselves, which tend to further an unlawful purpose.19