Grandpa in My Pocket is a British children's comedy television series commissioned by Michael Carrington for CBeebies, the BBC's dedicated pre-school and nursery channel targeting children aged 2–7 years. Based on the 1970s The Dandy comic adventure strip Peter's Pocket Grandpa by Ron Spencer (which itself was based on an earlier prose text story called Jimmie's Pocket Grandpa which had appeared in The Dandy in the 1940s), the programme stars James Bolam as a grandfather who owns a magical "shrinking cap", which only his 10-year-old grandson Jason Mason (played by Jay Ruckley) knows about. This cap enables him to shrink to about 4 inches tall, become a CGI-animated character, run very fast, and bring toys and objects to life. This allows him to experience many adventures which are narrated by Jason, including finding a prisoner under the floorboards, bringing a home-made robot to life, and driving Jason's toy car and biplane. The programme also stars Josie Cable, Zara Ramm and Sam Ellis, as Jason's sister, mother and father, respectively. According to the BBC press office, "Grandpa in My Pocket explores the hugely important relationship between grandchildren and grandparents by turning it on its head".Following the success of the first series in April 2009, a second was commissioned in March 2010, with a third filmed in 2011, after the third season, the series was assumed to have ended, however over 2 years later, a fourth season went into production, in the year 2013, before airing 4 years after filming commenced on the third season.

A fourth series was produced in 2013 with broadcast beginning in 2014.

The fourth season introduces some changes to the plot. Jason, who is now a teenager, has moved with his family into a windmill which they have opened as a hotel. Jason and Jemima's younger cousins Josh and Elsie (played by Harvey Thorn and Sezen Djouma) have come to stay for the summer, and the two become the series narrators as Grandpa decides to let them in on the secret of the shrinking cap.