Help → Install new Software → Switch to the Kepler Repository → General Purpose Tools → Marketplace Client
If you use Eclipse Luna SR 1, the released Marketplace contains a bug; you have to install it from the Marketplace update site. This is fixed again in Luna SR 2.
Marketplace update site:
- Luna – http://download.eclipse.org/mpc/luna
- Helios – http://download.eclipse.org/releases/helios
- Juno – http://download.eclipse.org/releases/juno
- Mars – http://download.eclipse.org/releases/mars