A few days ago I talked with someone about writing a book about TeX and we came to the question if *TeX* as a word and its Logo (and the related things like LaTeX, XeTeX, …, package names etc.) are (registered) trademarks or can I use it freely as any other word like dog, house, moon, …?

**Examples**

* using in book titles: *Start with TeX* or *Become a TeXnician* …
* using in corparate names: *LaTeX production company* or *TeX Help Line* …

Are there any restrictions in using “TeX” commercially (assuming the products/services are TeX related)?  

How about the derived words like “LaTeX”, “XeTeX” etc. 

**Edit:**
As Patrick said, the country could be important … I’m living in **Germany** and want to sell from there too but I could imagine that there are readers from Swiss and Austria for German books too.