Disney announced today that bookings for Walt Disney World Magic Your Way packages for 2018 will begin on June 20, 2017. It is worth remembering that Disney usually only allows you to book out Disney World trips 499 days in advance, so on June 20th, you will only be able to book trips through November 1st.
More information about booking a Walt Disney World Resort trip can be found here.
Update 6/20/17: You can now start booking 2018 Walt Disney World trips as of today. One interesting twist is the inclusion of alcoholic drinks in the Disney Dining Plan. More info about that can be found here.