What's in the Beatles Mono CD Box Set?

The Beatles First 10 UK Albums In Their Original Mono Mix
Through 1968 The Beatles mixed their albums in mono (as well as in stereo.) This is because at the time mono mixes were considered most important as most of The Beatles fans listened to their LPs on a mono playback system.

The first 10 UK albums (that's the original albums as The Beatles intended them to be heard) are included in their original mono mix (most of which have never been put on CD before) in this box set. That includes every Beatles album from 1963's Please Please Me through 1968's The Beatles (better known as The White Album.)

Including Magical Mystery Tour
Magical Mystery Tour is a somewhat controversial inclusion in The Beatles official UK album catalog because it was originally released as an EP (with 6 original songs) in the UK. In the US it was released as an LP with those original 6 songs combined with 5 previously released songs (such as "Strawberry Fields Forever" and "All You Need Is Love.")

In 1976, this US album version was released in the UK as it was becoming a popular import. Then when The Beatles catalog was put on CD in 1987, it was included along with the original UK albums.

Some Beatles purists insist that Magical Mystery Tour not be considered an official Beatles album, but at this point it's clear that it is being considered as such by Apple Corps and thus it is included in both the Mono Box Set and the Stereo Box Set.