The OED Online subscription is often expensive for individuals. Archive.org provides a legal way to access the older, out-of-copyright volumes for free.
The foundational work led by James Murray. It is the most common version found on Archive.org. oxford english dictionary pdf archive.org
This merged the original volumes and supplements into 20 volumes. Note that this version is still under copyright, so full PDFs are rarely available legally on public archives. The OED Online subscription is often expensive for
A condensed version that still retains the historical focus but is much easier to navigate in PDF form. Tips for Navigating OED PDFs It is the most common version found on Archive
You can easily find the first edition of the OED (originally titled A New English Dictionary on Historical Principles ). Since these were published between 1884 and 1928, they are in the public domain.
If you are studying Victorian literature, seeing the dictionary as it existed in the late 19th century provides insight into the linguistic mindset of that era.
These scans preserve the original typography and layout of the printed books, which many scholars find more intuitive than a database search result. Understanding the Different Versions