XCOM: Enemy Unknown is one of a new breed of games that comes without a manual or even a tech-tree, which makes planning research in advance a bit of a hassle. To that end, we've assembled a tech-tree for the game to remove some of the guesswork from your planning.
With the aid of the tech tree, you'll be able to plan your scientific research in advance and develop your soldiers and playthrough accordingly.
You should have less trouble in the game's Ironman mode if you can hatch a plan in advance.
Keep in mind that you'll need to construct the appropriate facilities in your base to conduct autopsies and interrogations. Many of the scientific advances also require significant alien resources to produce and Engineering manpower.
XCOM: Enemy Unknown is currently available for the PC, Xbox 360 and PlayStation 3. We reviewed the game here.
Credit: The tech-tree is inspired by agent86's XCOM: Enemy Unknown research.