A method of time-of-flight mass spectrometry is disclosed comprising: providing two ion mirrors (42) that are spaced apart in a first dimension (X-dimension) and that are each elongated in a second dimension (Z-dimension) orthogonal to the first dimension; introducing packets of ions (47) into the space between the mirrors using an ion introduction mechanism (43) such that the ions repeatedly oscillate in the first dimension (X-dimension) between the mirrors (42) as they drift through said space in the second dimension (Z-dimension); oscillating the ions in a third dimension (Y-dimension) orthogonal to both the first and second dimensions as the ions drift through said space in the second dimension (Z-dimension); and receiving the ions in or on an ion receiving mechanism (44) after the ions have oscillated multiple times in the first dimension (X-dimension); wherein at least part of the ion introduction mechanism (43) and/or at least part of the ion receiving mechanism (44) is arranged between the mirrors (42).