Building a capitol on a planet changes your home planet to the planet where you built the capitol. You may only have one Capitol per empire. Your home planet is immune to the spy missions Insurrection and Appropriate Technology. In addition, through the use of the Stockpile, you can build resource buildings past level 15 on your Capitol planet. As an added bonus the capitol produces a small amount of additional Happiness.
The Embassy allows the formation of alliances. It is also a prerequisite to building the Space Station. Each level of the Alliance Leader's highest-level Embassy allows 2 more members to join the alliance. Alliance members need only have a level 1 embassy to participate.
The Espionage Ministry allows the construction of spy pods, or, at level 15, spy shuttles, at the shipyard. It also allows better offensive training of your spies. The higher the building level, the more effective your spies will be applying their trade.
Intel Training Facility
Used to train spies in the ways of gathering intelligence.
The Intelligence Ministry is where you train and manage your new spies. You may train 3 spies per level of this building. You may only construct 1 Intelligence Ministry on a planet.
Mayhem Training Facility
Used to train spies in the art of destruction.
A black market for buying and selling well trained spies. The Mercenaries Guild can sell any spies from any planet in your empire as long as they are on the same planet where the Mercenanries Guild is located.
Network 19 Affiliate
The Network 19 Affiliate is your empire's source for up to the minute news in your region of the Expanse. Get updates on what other empire's are doing and what you'd prefer they weren't doing. The Network 19 feed can be manipulated through the use of of espionage and political policy. Well informed people are happy people so the network also produces happiness. The higher the building level the more of the expanse you can get news from and the more happiness is produced. Also if you use the option to restrict media the happiness normally generated by this building is instead subtracted.
The Observatory allows the construction of probes and colony ships at the shipyard. It also provides a list of all your active probes and the stars they are observing. A higher building level allows more probes to be constructed. You may only have one Observatory on a planet.
Politics Training Facility
Used to train spies in the dark art of social engineering.
The Security Ministry increases the effectiveness of your defensive spies. The higher the building level the more training your spies receive. It is also required to build defensive drone ships.
Theft Training Facility
Used to train spies in the art of appropriation.