A cartridge for an aerosol provision system comprising the cartridge and a control unit , wherein the system comprises a vaporiser for vaporising an aerosolisable material, wherein the cartridge comprises: a mouthpiece outlet ; an air channel extending from an air inlet for the cartridge to the mouthpiece outlet via an aerosol generation region; a reservoir for containing an aerosolisable material for aerosolising; an aerosol outlet tube (38;62), extending between the aerosol generating region and the mouthpiece outlet , for directing aerosol generated in the aerosol generating region through to the mouthpiece outlet , wherein the reservoir extends around the aerosol outlet tube (38;62); wherein the cartridge further comprises an aerosolisable-material-level observation means for allowing a user to observe a level of aerosolisable material inside the reservoir ; wherein the aerosolisable-material-level observation means comprises a portion of the cartridge, and wherein the portion of the cartridge forms a first wall portion of the reservoir ; and wherein a surface of the outlet tube (38;62) is visible from the portion of the cartridge ; wherein the cartridge comprises a first surface , a second surface , and a first side surface and a second side surface , wherein the side surfaces (209C;209D) are located between the first surface and the second surface ; wherein the first side surface and the second side surface are inclined towards the mouthpiece outlet ; and wherein the portion of the cartridge is located on both the side surfaces (209C:209D); wherein the portion of the cartridge further comprises: a first, elongate, window for viewing into the reservoir , wherein the first window is on the first side surface ; and a second, elongate, window for viewing into the reservoir , wherein the second window is on the second side surface ; wherein each window comprises a maximum dimension of no more than 20mm. a mouthpiece outlet ; an air channel extending from an air inlet for the cartridge to the mouthpiece outlet via an aerosol generation region; a reservoir for containing an aerosolisable material for aerosolising; an aerosol outlet tube (38;62), extending between the aerosol generating region and the mouthpiece outlet , for directing aerosol generated in the aerosol generating region through to the mouthpiece outlet , wherein the reservoir extends around the aerosol outlet tube (38;62); wherein the cartridge further comprises an aerosolisable-material-level observation means for allowing a user to observe a level of aerosolisable material inside the reservoir ; wherein the aerosolisable-material-level observation means comprises a portion of the cartridge, and wherein the portion of the cartridge forms a first wall portion of the reservoir ; and wherein a surface of the outlet tube (38;62) is visible from the portion of the cartridge ; wherein the cartridge comprises a first surface , a second surface , and a first side surface and a second side surface , wherein the side surfaces (209C;209D) are located between the first surface and the second surface ; wherein the first side surface and the second side surface are inclined towards the mouthpiece outlet ; and wherein the portion of the cartridge is located on both the side surfaces (209C:209D); wherein the portion of the cartridge further comprises: a first, elongate, window for viewing into the reservoir , wherein the first window is on the first side surface ; and a second, elongate, window for viewing into the reservoir , wherein the second window is on the second side surface ; wherein each window comprises a maximum dimension of no more than 20mm. a first, elongate, window for viewing into the reservoir , wherein the first window is on the first side surface ; and a second, elongate, window for viewing into the reservoir , wherein the second window is on the second side surface ; wherein each window comprises a maximum dimension of no more than 20mm. <EOS>