IFAB Laws of the Game (2020-2021): https://theifab.com/laws

Modifications to the Laws: https://theifab.com/laws/chapter/3

FIFA – Refereeing: https://www.fifa.com/what-we-do/education-and-technical/referees/

US Soccer Referee Program: https://www.ussoccer.com/referee-program

US Referee Connection: https://www.usrefereeconnection.com/

CNRA (California North Referee Administration): https://www.cnra.net/