Collectible items are present throughout the Resident Evil titles. In earlier games, these were only items that were unlocked after completing the game under certain conditions (e.g. an S rank, a higher difficulty or beating it a set number of times), but were none-the-less collected as a means of proving one's achievements, like the rocket launcher in the first Resident Evil. 2003's Resident Evil Outbreak introduced collectible "special items"; some of these would allow the player to unlock new costumes. Resident Evil 4 and Resident Evil 5 instead have "treasure items", which can be collected and sold in exchange for money, which is used for purchasing and modifying weapons.