Big Brother's Little Brother is a magazine television programme shown on Channel 4 and its sister digital channel E4 during a series of Big Brother in the UK. Commonly known as BBLB, it is presented by Dermot O'Leary. The programme looks at Big Brother-related activities outside the house, interviews celebrities, journalists and friends and family of housemates, and also the evicted housemates themselves.

Originally aired with the second series of Big Brother in 2001, and shown every Sunday morning as part of Channel 4's T4 slot, BBLB developed into a twice-weekly show with the third series of Big Brother. For the fourth and fifth series it was shown every weeknight at 5pm on E4 before being repeated for terrestrial viewers at 6pm on Channel 4. The Sunday programme includes the first interview with the most recently evicted housemate.

Starting with the fourth series, an extra clause was added into the contracts between contestants and producers Endemol which bound evictees to appearing on BBLB the Sunday after their eviction (they are evicted on Fridays) and every night for the next week. Any other appearances on BBLB or Big Brother-related programmes are optional.

In the fifth series, BBLB and Dermot campaigned for Stuart Wilson's cowboy hat to be returned to him after Big Brother removed it from the house. The campaign, which was born from a joke but turned 'serious', saw among other things viewers donating money to paste an advert on the billboard facing the Endemol studios so that BB execs would see it every day going to work.

Also, the Sunday after the finale of Big Brother 5, Big Brother's Little Brother held its first ever BBLB Reunion BBQ.