Cities XL's basic concept is simple: you must design a profitable city that will bring people and vitalize commerce. You do this by placing various services around the town, providing different measures of housing, and building up several different kinds of industry. Once your city really begins to grow, you will begin to gain more money through taxes and trade, which will let you expand. Repeat as necessary until you get bored, then wipe the slate clean and move on. The basic building structure of a city is house, then industry, then services to protect citizens, with things such as monuments, tourism-related activities, and other various distractions breaking up the monotony.

The most important concept in Cities XL, one which you don't learn until near the very end of the tutorial, is trade. Trade is where you generate tokens based on the production of your city, which you may then push out to other cities or an AI controlled corporation (humorously run by someone called Don Madolf). You may also import resources you lack the production for in order to normalize the city's economy as well. By engaging in trade, you will boost your revenue through the sale of various different products. This makes trade absolutely essential to your city, as you will quickly bankrupt without it. Trading is also essential in Planet Offer, which will be discussed later.

A touted feature of Cities XL is the ability to curve the roads. This may seem completely unimportant, and it is. Curved roads do little except look nice when looping around. They potentially open the way for you to make highway overpasses, but in reality, it's just a completely irrelevant feature that, quite confusingly, got a lot of hype time. The normal road creation is plenty good, and the ability to set "free zones" where you can place buildings and roads at any angle is a godsend. Why didn't they hype up the free placement instead of curves? The world may never know. Regardless, there are a fair amount of transportation options, although given the many different kinds of roads, there's not so much as a bus or subway station in sight.

The population of your city is comprised of four different classes: unqualified, which work in heavy industry, retail, and offices as grunt labor; qualified, which work as the managers, foremen, and other such slightly higher positions in industry and office work, as well as the laborers in cautious work such as high-tech industry; executives, which head up the larger businesses such as high-tech factories; and elites, which are the highest of the high, the 1% of the population that makes 90% of the money. Each population segment is used in a particular set of industries, which makes balancing the four very important if you want to build a successful city. Industries are likewise segmented, with the lower industries producing lots of pollution and the higher industries producing none. Every time the little circle fills, you will gain the population and money shown below each. For example, if you are producing enough goods to make +$6,000, this means you get $6,000 every tick of the timer. In single-player, this timer is adjustable, in Planet Offer it is not.

A cool feature of the game are the blueprints, which function very similar to the earned landmarks of SimCity. You get blueprints from the website or trading with other players, and each blueprint offers distinct benefits to your city, such as increasing satisfaction within a certain class of worker or increasing the amount of tourists. These blueprints require a certain amount of trade tokens from your city, which will advance the blueprint in phases until it is finally complete. It's the coolest part of the game, turning multiplayer into sort of a trading card game, but it is not implemented to a great extent quite yet.

Planet Offer is the multiplayer mode, and is the other major feature offered by Cities XL. It functions much like an MMO, with each player managing a city on their own and interact through trade or looking at other cities. It's interesting, but the subscription fee is a sort of slap in the face, since the features present most accurately resemble your average free browser strategy MMO. It's cool, but certainly not worth ten dollars a month, and is a bit laggy to boot. Along with Planet Offer comes the ability to make a player avatar using a set of controls that looks suspiciously similar to The Sims. However, where the tools in The Sims are excellent, the tools in Cities XL are not that good, and almost all the avatars look downright ugly if you actually take the time to do more than glance. You can run around in your city or somebody else's in your avatar, but there is little point.