Lego Stranger Things (stylized as LEGO Stranger Things) is a Lego theme based on the Netflix sci-fi horror series of the same name created by the Duffer Brothers. It is licensed from Netflix. The theme was first introduced in May 2019 with the latest set released in January 2026.

Lego Stranger Things was based on the Stranger Things 2016 Netflix sci-fi horror series, which focuses on the investigation into the disappearance of a young boy (Will Byers) amid supernatural events occurring around the town, including the appearance of a girl with psychokinetic abilities (Eleven). Lego Stranger Things aimed to recreate the main characters in Lego form, including Barbara "Barb" Holland, Eleven / Jane Hopper, Mike Wheeler, Lucas Sinclair, Dustin Henderson, Will Byers, Joyce Byers, Chief Jim Hopper, and the Demogorgon.

Lego senior model designer Justin Ramsden worked closely with Netflix to design The Upside Down set: "they gave us loads of behind the scenes images and plans." He said, "We also got the chance to create three new elements for the set as well, they are headgear for the Demogorgon, a hair piece for Dustin and also the hair for Will." He further explained, "With the Stranger Things set, we started off with a concept sketch. There was an elite team of LEGO designers that joined together to discuss what this model could be. From those meetings, one of the concept designers drew a quick sketch, and that became the basis for what the model could look like. We followed the sketch and had a close dialogue with Netflix. There was some back and forth with them, and we did iterations that made the set more stable, more playable, and with more functions."

In 2019, Lego Stranger Things theme was launched at The LEGO Store in Flatiron District, New York. Later, it also launched in the UK at Lego Store Leicester Square, London. As part of the marketing campaign, The Lego Group released The Upside Down (set number: 75810) based on a version of the Byers' home.

According to BrickLink, The Lego Group released two Lego sets as part of the Lego Stranger Things theme. The product line was eventually discontinued by the end of December 2022.

In 2019, The Lego Group had a partnership with Netflix. The Lego Group introduced a Stranger Things set called The Upside Down (set number: 75810), based on a version of the Byers' home, and its replica of the Upside Down was released in May 2019. The most extensive set consists of 2287 pieces with 8 minifigures. The Byers' house had four rooms: a front porch with furniture, a living room, a dining room, and Will's bedroom. It also included Chief Jim Hopper's police truck and a variety of accessories. The set included Lego minifigures of Eleven, Mike Wheeler, Lucas Sinclair, Dustin Henderson, Will Byers, Joyce Byers, Chief Jim Hopper, and the Demogorgon. The sets were designed primarily for adults with an age rating of 16+ or above. The set was designed by Lego Senior Model Designer Justin Ramsden. In 2021, The Lego Group announced The Upside Down (set number: 75810) was retired on 31 December 2021.

In July 2019, San Diego Comic-Con announced that an exclusive Barb minifigure would be given away to the winners.

In February 2022, a Demogorgon minifigure Keyring was released and was retired in August 2022.