Regulations are rules generally issued by agencies, generally part of the executive branch of government, and are the primary form by which administrative law is created. Agencies receive their authority to devise regulations from the legislative branch of government, through enabling legislation. Regulations are created at both the federal and state level.
On the federal level, the two major legal research resources are:
Regulations are first published chronologically in the Fed. Reg., which is published daily (except Saturday, Sunday, and official federal holidays). The final rules are then arranged by agency and subject in the CFR.
The chronology of the Fed. Reg., followed by the CFR, resembles that of statutes' publication chronology of the Statutes at Large, followed by the USC. The Fed. Reg. differs in that it contains a large amount of material related to the rulemaking process that does not appear in the CFR, which only publishes final rules.
In Texas, on the state level, there is the Texas Register and the Texas Administrative Code.
Any given area of law may involve statutes, regulations, and/or case law. These three types of primary law exist on both the federal and state level. Figuring out what primary law is on point to your particular issue can be difficult, which is why it is important to look for secondary sources first that pull relevant authority from all three branches of government, on both a federal and state level.
Of the three kinds of primary law to turn to after surveying secondary sources, it is usually best to research regulations after statutes, but before case law. Statutes provide the authority for agencies to create regulations whereas courts are called upon to interpret both statutes and regulations.
By this point in your research, you may already have citations to regulations from secondary sources or from researching statutory law. It is at this stage in the research that you will want to turn to regulatory sources to confirm that you have located all relevant regulations or to confirm that in fact your question does not involve regulatory law.
Regulations are available in print and online. Online sources include both free, such as from the federal government, and commercial, such as from Lexis and Westlaw. See this guide's individual subpages for further detail.
For more information about basic regulatory research, see Tarlton's legal research guide, "Finding a Regulation."