how long does the protection of a trademark last?

Answer 1

As the other user stated, a trademark can remain active forever as long as the proper steps are taken.

There are specific time lines you'll need to make yourself aware of (I'm assuming we're talking about the US - my apologies if this doesn't apply):

* Combined Declaration of Use & Incontestability under Sections 8 & 15

"You must file the Combined Declaration, specimen, and fee on a date that falls on or between the fifth (5th) and sixth (6th) anniversaries of the registration"

* Combined declaration of use in commerce/application for renewal of registration of mark under Sections 8 & 9

"You must file a Section 8 declaration, specimen, and fee on date that falls on or between the ninth (9th) and tenth (10th) anniversaries of the registration, and each successive ten-year period thereafter...Also, you must file a renewal application within the same period..."

http://www.uspto.gov/teas/eTEASpageC.htm -- Link to above info

Hope that helps!

Answer 2

Looks like TM Express got all the right info.

Answer 3

Forever, as long as you actively use, maintain and protect it.