I'm surprised at some of the responses in this thread. Immortal is the most common difficulty I play, and I actually think its a relatively small gap between emperor and immortal. I find the gap between king and emperor to be the greatest, followed by the gap between immortal and deity. In my experience the extra AI settlers add the most difficulty. When going from emporer to immortal, the AI gets one extra warrior and one extra builder. You will tend to have the same amount of space to expand into on the two levels, but the AI can put a little bit more pressure on you in the early game, so you need military units. Speaking of military units, I used to make the mistake of building nothing but slingers, but you want to build warriors to park out in front of your cities to block the AI from attacking your city centre from multiple tiles in a turn. Also, don't get caught off guard by an early AI attack. If you see them march a single warrior toward your borders, you can expect an attack 90% of the time. If they send two military units near you its pretty much a certainty. Some other strategies to be aware of: -Sell the AI luxury resources as soon as possible. They have a lot of gold, and being able to by turns worth of production in the early game is a life saver. My standard openings lately has been to purchase my first builder. -Place districts as soon as they are available even if you don't want to build them right away. This locks them in at a cheaper price.