The "Adventure Time Theme Song" and opening title sequence features all of the main characters and also some of the minor characters. The theme is sung and played by series creator Pendleton Ward. It has the same lyrics as the animated short but there are some slight variations.
The opening title sequence starts with a view of a post-apocalyptic wasteland that features a rat inside of a broken television and several undetonated nuclear bombs. Next, in a snow-covered biome, are shown penguins, including Gunter and two other penguins hugging (with a tiny red heart floating above their heads) that make a few quick quacking sounds, and a Snow Golem sitting on a grassy hill nearby. Then the rest of the Ice Kingdom appears including Ice King flying next to his lair, spinning around to face the screen while activating his Ice Powers with his hands. It shows the Candy Kingdom and a large crowd of Candy People laughing and dancing in the middle of the road. After that, the camera quickly scales Princess Bubblegum's Castle, eventually passing the clouds to where we can see Princess Bubblegum as she smiles and waves while riding on the back of Lady Rainicorn. The camera then pans to the right, and zooms into a mountain range showing Marceline playing her Fender Precision Bass while sitting outside of her cave. She turns and hisses at the audience while showing her pointy teeth. Then outside of Finn and Jake's treehouse is the two-headed duck. The ending shows Finn and Jake's Tree Fort and then the two of them inside. BMO is seen sitting nearby. Finally, they pound their fists together and a loud smashing sound is heard as the theme song begins. This entire ordeal occurs approximately within the span of 12 seconds. When the show's title is seen, Finn (without his green backpack) and Jake float up using feathered wings sticking out from their backs while holding a white piece of cloth that says with Finn and Jake. Then, they are seen going somewhere as the lyrics go "C'mon grab your friends," and then Jake winks when the lyrics "Jake the Dog" come up, and Finn seems to bark and stick his tongue out when the lyrics "Finn the Human" come up. The sequence ends when Finn and Jake reach the top of a rocky mountain that they were climbing. Finn gets to the top and strikes a victorious pose while Jake lies down near Finn as the show begins.
The lyrics with ukulele chords to the theme song are as follows:
|D||C'mon grab your friends,|
|C||We're going to very|
|D||distant lands. With|
|G||Jake the Dog and|
|D||Finn the Human,|
|C||The fun will never|
|D||end, it's Adventure|
- During the post-apocalyptic wasteland scene, you can see a gray arm with purple spots and a bite mark coming out of the tree that has axe and arrows in it. It has been confirmed to be a zombie arm.
- In Issue 1 of the Adventure Time comic, it can be seen that Jake was actually filming the opening sequence.
- Before Marceline opens her mouth, her fangs are blunt. This is also seen in the episode "Daddy's Little Monster."
- In both versions, (Fionna and Cake and Finn and Jake) a two headed duck can be seen right in front of the tree fort.
- In the Spanish (Latino) version, when the singer says Jake's name it sounds as if she is rushing. This might be because the song and pictures were going in a fast pace.
- Only four different versions of the intro are seen so far, the first is in "Fionna and Cake" (and "Bad Little Boy" and "The Prince Who Wanted Everything"), the second is in "A Glitch is a Glitch," the third is in "Food Chain," the fourth is in "Bad Jubies," and the fifth in the Adventure Time Mini-Series: "Stakes".
- The Arabic, Bulgarian, Danish, Hindi, Japanese, Russian, Spanish (Latino) and Swedish versions of the intro use more than one voice when singing the theme song.
- In Russia, both the original and gender-bent versions of the theme song are sung by the same voice actor (also the voice of Lumpy Space Princess and other background characters).
- Starting with the episode "Bonnie & Neddy," the subtitle "A Cartoon Network Original" appears on top of the title.