Do I need a new zone for each domain I have on my server?

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http://unix.stackexchange.com – I currently have a working BIND nameserver Running on my dedicated ubuntu server box. I have one zone set up.. example.com with its own nameservers. If I want to add a new domain to point to the server, can I somehow add it to the existing zone? Or do I have to create a new zone and setcoms nameservers to example.com? (HowTos)