If you have found a regulation and are trying to figure out why it was passed, to determine the agency's motivations for creating the rule or to discover whether the agency took into consideration certain issues when considering the rule, look in the Federal Register. This is equivalent of doing a legislative history for a statute. The key documents from the Federal Register are the Notice of Proposed Rulemaking and Notice of Final Rulemaking.
The Notice of Proposed Rulemaking includes information from the agency about the purpose of the rule and what the agency hopes to accomplish by its promulgation.
The Notice of Final Rulemaking includes information about the purpose of the rule, as well as a summary of the comments it received during the notice and comment period. Agencies may include a section called “analysis of comments and changes” that explains how the department changed the language of the rule as a result of the comments it received.
A rule published in the CFR will include a citation to the Federal Register where the final rule was initially published.
See example of regulation published in the CFR at left.
This is an excerpt of 14 CFR 129.101. Note the citation to 67 FR 79824 where the rule was first published and 68 FR 42882 where the notice of amendment was published.