From Sweden

You travel with the Eckerö Line´s ferries that leaves daily, all the year round. The ferries depart from Grisslehamn in Roslagen and arrive at Eckerö after 2 hours.
Finnlines from Kapellskär 
Viking Line from Stockholm 

From Finland

You travel by ferry Viking Line/Tallink-Silja/ Finnlines  or by aeroplane  from Åbo or Helsinki to Mariehamn and continue by car or bus to Eckerö, which you will reach after approximately half an hour.
(From Långnäs harbour by car to Eckerö takes 1 hour).

From Estonia

By Tallink-Silja ferry to Mariehamn.