The Palace trio were rewarded for their fine form at club level this season with international recognition.
For Guehi and Mitchell, it represents a first call-up to the senior side, the former having captained the Young Lions at Under-21s level in the past.
Gallagher won his first cap against in the remarkable 10-0 victory in San Marino last year.
All three will hope to make their mark as England take on Switzerland (Saturday, 26th March) and Cote d'Ivoire (Tuesday, 29th March) - the latter could see them come up against Wilfried Zaha.
Check out the best photos from their arrival at St George's Park and their first training session with Gareth Southgate's side in the gallery!