An infant sleep bag (100, 300, 400), comprising: a main body (101, 401) to receive the torso and legs of an infant, the main body including arm hole openings (103, 105, 215, 217, 305, 307, 605) arranged on either side of the main body (101, 401) and including respective arm closure mechanisms (102, 104) to allow the arm hole openings (103, 105, 215, 217, 305, 307, 605) to be in an open configuration in which the arms of an infant can pass through the arm hole openings (103, 105, 215, 217, 305, 307, 605), or a closed configuration in which the arms of an infant are maintained within the sleep bag, wherein the arm closure mechanisms (102, 104) comprise closure mechanisms (211, 213, 603a-c) provided on flaps or wings (212, 214, 603) that are integral or attached with the rear of the sleep bag, and corresponding closure mechanisms (601a-c) on the front of the main body of the sleep bag, wherein when the arm hole openings (103, 105, 605) are in the closed configuration, the flaps or wings (212, 214, 603) are folded over to enable the closure mechanisms (211, 213, 603a-c) provided on the flaps or wings (212, 214, 603) to engage with the corresponding closure mechanisms on the front of the main body (101, 401), wherein when the arm hole openings (103, 105, 605) are in the open configuration, the flaps or wings (212, 214, 603) are folded back over themselves to maintain the closure mechanisms (211, 213, 603a-c) provided on the flaps or wings (212, 214, 603) behind the main body (101, 401) such that they do not come into contact with an infant or their arms, and wherein the flaps or wings (212, 214, 603) are biased or configured to stay in the position in which they have been folded. a main body (101, 401) to receive the torso and legs of an infant, the main body including arm hole openings (103, 105, 215, 217, 305, 307, 605) arranged on either side of the main body (101, 401) and including respective arm closure mechanisms (102, 104) to allow the arm hole openings (103, 105, 215, 217, 305, 307, 605) to be in an open configuration in which the arms of an infant can pass through the arm hole openings (103, 105, 215, 217, 305, 307, 605), or a closed configuration in which the arms of an infant are maintained within the sleep bag, wherein the arm closure mechanisms (102, 104) comprise closure mechanisms (211, 213, 603a-c) provided on flaps or wings (212, 214, 603) that are integral or attached with the rear of the sleep bag, and corresponding closure mechanisms (601a-c) on the front of the main body of the sleep bag, wherein when the arm hole openings (103, 105, 605) are in the closed configuration, the flaps or wings (212, 214, 603) are folded over to enable the closure mechanisms (211, 213, 603a-c) provided on the flaps or wings (212, 214, 603) to engage with the corresponding closure mechanisms on the front of the main body (101, 401), wherein when the arm hole openings (103, 105, 605) are in the open configuration, the flaps or wings (212, 214, 603) are folded back over themselves to maintain the closure mechanisms (211, 213, 603a-c) provided on the flaps or wings (212, 214, 603) behind the main body (101, 401) such that they do not come into contact with an infant or their arms, and wherein the flaps or wings (212, 214, 603) are biased or configured to stay in the position in which they have been folded.