There are maximum and restriction depending on your income. 

See IRS publication 590 for limits.  Google it to determine your eligibilities.

Depending or your Adjusted Gross Income you could do both, however you might not be able to max out both account for a given year.

For me I choose to max out my Roth and do a partial 457 Deferred Compensation.  In my situation I cannot do take the deductible Traditional IRA.  Your situation will most likely be different.