I have a canon xsi, will my 18-55 lens from that camera fit a t5i body?

[cicopo]

YES

[TCampbell]

The T5i is an EOS camera.  It can use nearly any Canon EOS lens.  

EOS lenses come in two major categories... the "EF" lenses and "EF-S" lenses.   But somewhat recently Canon started offering mirrorless cameras and they built a few special lenses called "EF-M" lenses which only work on the mirrorless bodies.

That means your camera can use any EOS "EF" or "EF-S" lens in the Canon lineup.  It can also use the specialty lenses such as the "TS-E" (tilt-**bleep**) and "MP-E" macro-photo lenses which for purposes of compatibility are treated just like "EF" lenses.

Bottom line... use any Canon EOS lens as long as it is not an "EF-M" lens (but there are not very many EF-M lenses offered.)

One more thing...

If you bought any third party lenses (Sigma, Tamron, Tokina, etc.) then there is a possibility of a compatibility issue.  Canon does not publish the interace specs that allow the camera body and camera lens to communicate via the electronic connection.  The third-party companies "reverse engineer" this interface.  They then build their lenses and test those lenses using the Canon bodies which happen to be available at the time when that lens was designed.  From time to time (it's rare, but it does happen) Canon will come out with a new camera body which uses an aspect of the communication protocol that the third party vendor had never encountered before... and the lens will not perform as expeted.  Of course, those lensmakers are still in business and still making newer lenses.  That means they probably do know how to handle those communications today even if they did not when an older lens was built.  Some third party manufacturers can either "re-chip" or "re-flash" the firmware to update an old lens so that it continues to work with modern camera bodies.

If you have a Canon brand lens, you wont have a problem.  If you have a 3rd party lens, you *might* encounter a problem (usually not -- but it does happen).  And if you do encounter a problem, the manufacturer of the 3rd party lens *might* be able to update it.