Here are the most recent versions of libpqxx, in source-code form. Binary packages are typically available from a package maintainer for your particular platform.
More download sources:
- Development snapshots
- All releases
- All releases (FTP)
- Ubuntu private package archive
- PostgreSQL RPM packages
To check out the current development tree, check out svn://pqxx.org/libpqxx/trunk/ using the Subversion revision control system. More detailed instructions on the UsingThisSite page.
It's not automated yet, but there are also occasional Ubuntu packages of the development snapshot on Launchpad.