Castlevania: Aria of Sorrow is a 2003 action role-playing game developed by Konami Computer Entertainment Tokyo and published by Konami for the Game Boy Advance. It is the 20th main entry in the Castlevania series, as well as the third and final game produced for the system. Producer Koji Igarashi, who had led the production teams for previous Castlevania games, oversaw Aria of Sorrow's development in parallel with its predecessor Castlevania: Harmony of Dissonance (2002). Michiru Yamane returned to compose the music alongside Takashi Yoshida and Soshiro Hokkai. Director Junichi Murakami was new to the Castlevania series.

In contrast with other Castlevania titles taking place in the late medieval period or the early 20th century, Aria of Sorrow is set in 2035, decades after a climactic war resulted in Dracula's permanent demise and his castle being sealed in a solar eclipse. The plot follows the journey of Soma Cruz, a teenager granted occult powers, as he is trapped in the eclipse and encounters dark figures who wish to inherit Dracula's power. The game has been described as an action-adventure game with elements of role-playing games. Aria of Sorrow introduces several features to the series, such as the "Tactical Soul" system that enables Cruz to absorb the properties of defeated enemies, as well as a full New Game Plus mode.

Aria of Sorrow was released in May 2003. Although it sold poorly in Japan, selling 27,000 units nearly one month after its release, it was commercially successful in the United States, with more than 158,000 units sold in the three months following its release. Aria of Sorrow received universal acclaim, with praise for its visuals, gameplay (particularly the Tactical Soul System), music, and level design. Some critics considered it the best Castlevania game since Symphony of the Night (1997), as well as one of the best Game Boy Advance and Metroidvania genre games.

Konami released a sequel, Castlevania: Dawn of Sorrow, in August 2005. It incorporated many elements from its predecessor, including the "Tactical Soul" system. Aria of Sorrow was re-released as part of the Castlevania Advance Collection on September 23, 2021 for the Nintendo Switch, PlayStation 4, Windows, and Xbox One alongside Castlevania: Circle of the Moon (2001), Harmony of Dissonance, and Castlevania: Dracula X (1995).

Aria of Sorrow features a 2D side-scrolling style of gameplay where the player controls the onscreen character from a third-person perspective. The game has been described as an action-adventure game with role-playing elements such as characters levelling-up each time they earn a set number of experience points from defeating enemies; each "level" gained increases the character's statistics, thus improving their performance in battle. Statistic examples include hit points, the amount of damage a character can receive; magic points, which determine the number of times a character can use magical attacks; strength, the power of a character's physical attacks; and intelligence, the power of a character's magical spells. Upon encountering an enemy, the player can use a variety of weapons to attack and defeat the enemy. Despite the game being set in 2035, the available weapons are largely medieval, including swords, axes, and spears; though a handgun is available. These weapons differ in their damage output, the range of the weapon, and the speed of the attack. Items and other accessories can be found by defeating enemies or by purchasing items from the game's shop.

Similar to previous games in the series, Aria of Sorrow is set within Dracula's castle, which is divided into several areas that the player traverses. These areas feature different components, such as different enemies, varying terrain characteristics, and a unique piece of theme music. Similar to most platform games, progression between areas is limited by the abilities the player has. While the method in which the player progresses through the game is initially linear, the player's options become more diverse as the number of character abilities increases.

Aria of Sorrow introduces the Tactical Soul ability system to the Castlevania series. It involves absorbing the souls of enemies in order to gain additional abilities. Save for a few exceptions, all types of enemies in the game can eventually yield a unique soul that can be absorbed by the player. The rate at which enemies' souls are obtained varies between enemies. Players can trade souls between two Aria of Sorrow cartridges using two Game Boy Advance consoles and a link cable.

Souls provide a variety of effects, and are separated into four categories: Bullet, Guardian, Enchant, and Ability souls. Bullet, Guardian, and Enchant souls are identified with the colors red, blue and yellow respectively, and the player can only have one of each type equipped at any given time. Bullet souls are Soma Cruz's replacement for sub weapons in this game, and enable the player to consume a set number of magic points to use an ability, often some form of projectile. Guardian souls provide continued effects, including transforming into mythical creatures and summoning familiars. Guardian souls continually drain magic points as long as they are active. Enchant souls are continuously active as long as they are equipped, and provide either an increase in statistics, or abilities such as the ability to walk on water. The fourth type, Ability souls, are treated differently from the other three types. They originate from one-of-a-kind enemies in the game, and once obtained, they remain active as long as the player does not specifically disable them, not consuming any magic points.