What Pub 15 covers
IRS Publication 15 is the agency's plain-English explanation of the topic in its title. The IRS produces dozens of publications, but only a handful are essential for a small-business owner to recognize. Pub 15 is one of them. It is updated each year shortly after the close of the prior tax year, and the current edition is freely downloadable as a PDF from IRS.gov. The opening chapters set out the legal framework — the Code section, the relevant Treasury regulations, and the leading court cases — and the later chapters walk through worked examples drawn from common fact patterns.
Who should read it
Pub 15 is most useful for the small-business owner or self-employed filer whose facts touch the topic in any meaningful way. That includes the first time you encounter the issue (when the publication serves as an orientation), each year as a refresher (when annual updates frequently change limits, rates, or thresholds), and any time you are weighing an election that the publication discusses. Tax preparers, enrolled agents, and CPAs treat Pub 15 as a first reference; sophisticated taxpayers can do the same.
How it fits with the other authorities
IRS publications are not law. They explain the IRS's interpretation of the underlying Internal Revenue Code, regulations, revenue rulings, and revenue procedures. In practice, the publication is usually a faithful summary of the controlling authority, but in close cases the controlling authority wins. A small-business owner whose facts sit near the boundary of a deduction, election, or credit should escalate from Pub 15 to the relevant Code section, regulation, or revenue procedure — and, if the dollars are large, to a tax professional who can evaluate the full record.
What changes year to year
Each annual edition of Pub 15 updates inflation-adjusted dollar limits, references to current-year forms, and any legislative changes from the prior year's tax bills. The substantive framework usually does not change. When it does — as with the Tax Cuts and Jobs Act in 2017, the SECURE Act in 2019, the CARES Act in 2020, or the Inflation Reduction Act in 2022 — the publication explicitly flags the change in its "What's New" section at the front, which is the single most useful page in the document for an experienced reader.
Practical tips for using the publication
Read the table of contents first to map your facts to a chapter; read the "What's New" page to catch any changes; and use the worked examples (typically late in the publication) as the fastest way to understand how the rules play out. Bookmark the PDF rather than printing — the IRS reissues each publication every winter and printed copies go stale within weeks of release. When citing the publication in a workpaper or memo, include the publication number, the year, and the page number to make it easy to verify.