Trainers need to collect a certain number of Gym Badges in order to qualify for a region's Pokémon League. Young Trainers usually begin their initial Pokémon journey by traveling from city to city in order to collect them. Badges are small enough to fit easily between one's thumb and index finger and can be pinned to a shirt or kept in a Badge case.
A selection of familiar and unfamiliar Badges can be seen in early character artwork by Ken Sugimori. It appears that the original concept of Badges was more similar to an embroidered patch than the pinned badge they are portrayed as in the anime and subsequent game entries. While some of these patches do resemble Badges seen in the final game like the Cascade Badge, the Volcano Badge or even the RainbowBadge, others don't appear to be based on anything, and may have only been made for the sake of aesthetics, much like real-life embroidered patches, such as Red's "LeafBadge" or Silver's "Artsy Badge".
Other instances of embroidered "Badges" can be seen in the cover art for the Games That Stand Out Collection magazine, with the male Trainer's rock or diamond badge and the female Trainer's teardrop badge, which shares a resemblance to the Cascade Badge. However, given the nature of this illustration (the designs were made specifically for this cover and weren't intended to be used in the franchise), it is likely that these designs were chosen randomly. The latter Badge's resemblance to the Cascade Badge was most likely a coincidence, given it is a stylized drop of water.
In Generations I-III, some Badges boost a certain stat or stats of the player's Pokémon. This boost is applied only in internal battles, not link battles. In Generations I and II, the stat or stats are increased by 12.5%; in Generation III, the stat or stats are increased by 10%. This boost does not exist from Generation IV onward.
In Generation I, this boost is reapplied whenever the player's Pokémon's stats are raised or lowered, allowing boosts to be stacked (this stacking effect is lost if the Pokémon levels up). In Generation II, if the attack is a critical hit and the attacker's used offensive stat stage is less than or equal to the opponent's defensive stat stage, all Badge boosts are ignored.
Note that in Generation I the game states that the Thunder Badge raises Speed and the Soul Badge raises Defense, but these are not the actual effects caused.
In Generation II, every Badge boosts the power of the moves of a certain type by 12.5% (1/8), despite never being referenced in the games. The type strengthened matches the type theme of the Gym (for example, Zephyr Badge boosts the Flying-type). These boosts work similarly to the way same-type attack bonus (STAB) boosts work, and are, in fact, calculated in-between weather modifiers and STAB.
Just like stat boosts, type boosts are not applied in link battles.
While Trainers can teach their Pokémon HM moves and use them in battle, Trainers require the appropriate Badge to use them in the overworld in GenerationsI through IV as well as Generation VI. In Generation V only, Badges are not needed to use HM moves in the overworld.
Poké Mart stock
From Generation IV onwards, the number of Badges a Trainer possesses affects which items Poké Marts sell. The more Badges, the more items that become available for purchase, with more expensive items generally appearing after more Badges are obtained.
In the games, in order to enter the Pokémon League and challenge the Elite Four and Champion, the player must have all eight Badges from that region (or in the case of the Indigo Plateau, either Kanto or Johto). In Unova, Kalos, and Generation I/III Kanto, Badges are checked individually through a series of Badge Check Gates; in Hoenn, Sinnoh, and Generation II/IV Kanto, Badges are checked all at once.
List of Badges
In Generation IV, these badges do not affect stats.
It is shaped like three raindrops arranged in a triangle.
When Badges are touched in the games, they play a single note, and will make a musical C major scale when all eight Badges are collected. When a player rubs the stylus across them numerous times to polish them (as they gradually tarnish), they will begin to shine. This process can be continued until four sparkles are visible. The musical notes are also the most clearly defined and accurately tuned when there are four sparkles.
Unlike other generations, it is the number of Badges that determines which outsider Pokémonobey the Trainer, rather than the Badges themselves (this distinction is important owing to the fact that the order of obtaining the Cobble, Fen, and Relic Badges can differ). For every second Badge the maximum level of obeying Pokémon increases (0 Badges—level 10; 2 Badges—level 30; 4 Badges—level 50; 6 Badges—level 70; 8 Badges—level 100). The number of Badges collected also affects the items that the player can purchase in Poké Marts.
Unlike previous Badges, the level at which traded Pokémon will obey the player goes up by ten per Badge, rather than the previous system of rising twenty levels after every even-numbered Badge. They can be polished like Sinnoh's Badges, although they do not make different notes when polished at the same level. Instead, the picture of the Gym Leader from whom the Badge was earned gets grayer.
In Black 2 and White 2 the Badges no longer dull over a period of time, and Sinnoh's notes were reintegrated into the Badge screen.
Although Badges are not required to use any of the HMs outside of battle, some HMs cannot be obtained until after obtaining certain Badges. However, as they are not required, traded Pokémon that have learned an HM move in another game can still use the HM move before acquiring any Badges.
It is shaped like a bow tie, similar to those worn by the Striaton Gym Leaders. It may also bear a resemblance to an opened pea pod, which contains two large peas; one green and one blue, with a smaller red pea at the center.
The Gym Leader faced depends on the starter Pokémon the player chose.