From the Introduction:
It can seem like lobbyists run Washington from behind the scenes. But their work isn’t completely opaque. They’re required to register with the House and the Senate when they lobby for a new client. Former members of Congress, former congressional staffers and former high-level regulators who now work as lobbyists—the so-called “revolving door” — are required to disclose their “covered” former positions. You can use this database to find out who’s lobbying on whose behalf — and about what issues.
The database is updated daily.
Direct to New ProPublica Lobbying Database
Direct to ProPublica Lobbying Database User Guide
See Also: Open Secrets Lobbying Database