Air

from Boston Logan International Airport (BOS)
55 miles / 1 hr drive to Portsmouth/Kittery

from Manchester, NH (MHT)
48 miles / 50 min. drive to Portsmouth/Kittery

from Portland International Jetport (PWM) 
51 miles / 53 min. drive to Portsmouth/Kittery

Amtrak

There is no train station in Portsmouth, but there are three stations nearby from which you can Über. 

Durham, NH (12.1 mile cab ride to Portsmouth)

Dover, NH (13.6 mile cab ride to Portsmouth)

Exeter, NH (13.7 mile cab ride to Portsmouth)

Greyhound

Portsmouth Bus Stop
54 Hanover St.
Portsmouth, NH 03801

North Carolina/Florida Travelers: 

Portsmouth International Airport (PSM) is a tiny local airport with seasonal flights from Raleigh/Durham and Florida on Allegiant & Breeze airlines