You can gain access to new Buildings, units, and services by negotiating new Contracts. You will automatically be awarded with a randomly selected new contract referral towards a new private military contract each day you visit your base. To unlock the actual Contract all the referrals required in its set must be collected. Specific Contract referrals can be purchased from any of the available Contracts that are currently uncompleted and unlocked from the Black Market's Referrals tab. Referals that you need can also be purchased using Influence Points and Diamonds.
Contract 1: Coloniel Waiguru
Contract 2: Emilio Tessinger
Contract 3: Early Retirement
Contract 4: Loose Cannon
Contract 5: Good Samaritan
Contract 6: Recover and Eliminate
Contract 7: A Day Late and a Dollar Short
Contract 8: Inside Job
Contract 9: Collateral Damage
Contract 10: Mixed Signals
Contract 11: Blame No One
Contract 12: Imminent Threat
Contract 13: On The Run
Contract 14: Extreme Prejudice
Contract 15: Plausible Deniability
Contract 16: Dangerous Liaisons
Contract 17: Ghosts
Contract 18: Old Friends
Contract 19: Revelations
Contract 20: A Change of Plans
Contract 21: Loose Ends
Contract 22: Project Torchlight
Contract 23: Playing God
Contract 24: Unfortunate Casualties