Upin and Ipin are five-year-old identical twin brothers living in a Malay-Muslim household with their sister Ros and maternal grandmother Mak Uda ("Opah"). They are orphans (in episode six, the twins, Ros and Opah were seen visiting their parents' graves), and they live in a village known as Kampung Durian Runtuh in Malaysia.

The first two seasons show the young twins' ordeal with Ramadan, the most venerated lunar month in Islam in which the faithful oblige themselves to abstain from consuming any food and beverage from dawn till dusk in every day of this period. Opah is seen as the boys' main source of significant religious and traditional wisdom. Despite the hunger from fasting, Upin and Ipin still maintain their mischievous tendencies which tends to annoy Ros.

In season one, not only were they induced by their elder sister and grandmother in honouring the holy month. Their friends, including some non-Malays, helped to keep their religious obligation in check. In season two, Upin and Ipin are already in kindergarten, having made some new friends. This time, they are more prepared and delighted to usher in the month of Ramadan.

In February 2009, the premise was extended to the big screen under the name "Geng: Pengembaraan Bermula" ("Gang: The Adventure Begins" with the word "gang" often colloquially used in Malaysia to represent a group of friends or people