Dear …

I am honored that you would ask me to __(be the keynote speaker at/emcee/etc.)__ your __(type of event)__. It is a noteworthy __(event/seminar/etc.)__ and I have no doubt it will be a great success. Regrettably, however, I must decline your invitation.

__(Briefly describe why you cannot accept – example: This type of event does not fit in well with…/My schedule will not allow me to participate…/etc.)__. Please accept my regrets and kindly pass along my good wishes to all those involved. I sincerely hope all goes well for you and that it is a tremendous success.

Best regards,