The holiday season has arrived, and for parents that means trying to track down the hottest toys of the year. (On the other hand, if you’re the nostalgic type, these are 25 discontinued classic toys you can probably still find.)

24/7 Tempo has compiled a list of 21 of the most popular gifts of the century. The list was assembled using the archives of companies such as Hasbro, data curated by The Strong National Museum of Play, encyclopedia sources such as Britannica, and media outlets including Reader’s Digest, The New York Times, Time, Good Housekeeping, and Smithsonian. 24/7 Tempo also exercised editorial discretion where appropriate.

For toy companies looking to sell the hot toy of the holiday season, it’s a matter of timing, accurately assessing the mood of the public, selling something that’s innovative, or marketing something that’s a novelty. 

In recent years, many of the most popular toys have featured the latest tech bells and whistles. Among these are a robotic dog (Tekno the Robotic Puppy) and a biomorphic humanoid (Robosapien) that was developed by a former NASA employee. 

Technology has become an integral part of childhood learning with toys such as LeapPad Explorer, and an iPad-like tablet for children (plus the actual iPad). XBox, Nintendo Wii, and Guitar Hero all helped transform how games are played in our leisure space. (These are the best-selling Nintendo games of all time.)

Click here to see 21 of the most popular gifts of the century

The holiday season wouldn’t be the holiday season, if the demand for certain toys didn’t create  a furor. That was the case with Zhu Zhu Pets, which are programmable toy hamsters that mimic the unpredictable behavior of the real animal. They became an instant sensation over the holidays in 2009. The demand for Hatchimals – mini-figure robotic furry, bird-like creatures that “hatch” themselves from an egg – was so intense in 2016 that Spin Master, the Toronto company that created the toy, flew them in from its Chinese factories.