Originally posted by: Aikouka
Originally posted by: Baked
You need Classic before you can install TBC, and TBC before you can install WLK. You can't skip.
It is good to note that you probably don't even need that much initially anyway. If you do not want to play as a Draenei (space goat) or a Blood Elf (metrosexual), then you don't need TBC. Although, this means you cannot play a Shaman on the Alliance faction or a Paladin on the Horde faction as those are specific to the aforementioned TBC-only races. If you do not wish to play as one of those, you can simply buy the original and there's no real reason to buy TBC until level 58, which is when you can enter the Outlands on your own accord. Note that I put that stipulation, because you can be summoned or take a Mage-created portal at any level.
You don't need Wrath of the Lich King until you hit 55 or 68. The level difference depends on if you want to play a Death Knight or not, because you must have at least one level 55 character on any server to create a Death Knight, which requires the Wrath of the Lich King expansion. Also, be aware that I did mention level 58 as a time to get TBC above... and as Baked mentioned, you will need TBC to install WotLK (it says this on the box as well). If you do not wish to play a Death Knight, then you are able to head to Northrend at level 68 on one of the various boats or zeppelins. Just like before, you can receive a summon or take a Mage portal before this level though.