If they are beating down the doors to get you to interview with their company, this letter will let them down easy.
Free to download and print.
Dear {Name},
I was very flattered to receive your request to interview for the {position} position at {Company Name}. I have been hearing incredible things about your organization since {subject} in {year}. However, I am currently happily employed at {Company}.
Thank you for thinking of me, and I hope you'll keep me in mind some other time in the future.
Sincerely,
{Name}