PatentsView
PatentsView is run by the USPTO to make US patent records easier to explore and analyse. It links patents to the people, organisations, and places behind them, and keeps the database updated on a regular schedule.
There are two main ways to work with it. The Data Download provides the complete US patent collection as data tables that you can join together or text-mine, which the maintainers recommend for heavy-duty use. The API is better suited to lightweight, regular queries: it allows each user up to 45 queries per minute and returns the full text of title and abstract sections along with inventor, assignee, location, and classification details.
The data is released under CC BY 4.0, so you can use it commercially as long as you credit the source. That makes it one of the more straightforward patent corpora to build on.
Related sources
EPO Espacenet & Open Patent Services
Free access to over 140M patent documents from the European Patent Office (EPO). Its Open Patent Services text analysis tools have made patent full texts much easier to reach, though the terms are open access rather than an open reuse licence.
Google Patents Public Datasets
A query-based collection of over 120M patent documents from more than 100 patent offices worldwide, including applications, pre-grant publications, and granted patents. Accessible through Google BigQuery, with hundreds of millions of USPTO events also queryable.
Harvard USPTO Patent Dataset (HUPD)
A large-scale, structured corpus of US patent applications built specifically for machine learning and natural language processing research. It fills the gap left by mainstream patent search tools, which are not designed with the ML and NLP community in mind.
WIPO PATENTSCOPE
A search service for international patent collections, maintained by the World Intellectual Property Organization (WIPO). It lets you search across patent applications filed under international treaties alongside national collections from many countries.