A hair clipper apparatus comprising: a hair clipper having a housing and a cutting element; and a comb (200, 300, 300'), the comb (200, 300, 300') comprising: a comb portion (208, 308, 308') configured to be arranged forward of the cutting element of the hair clipper in a cutting movement direction (x) of the hair clipper, the comb portion comprising a plurality of comb teeth (216, 316) having slots (218, 318) formed there between for guiding hairs to be cut to the cutting element, wherein rear edges of the comb teeth, which face the housing of the hair clipper in use, define a first rear comb surface (324, 324') proximate the cutting element in use and a second planar rear comb surface (328, 328') ultimate the cutting element in use, and wherein the first spacing angle (θ1) is formed between the first rear comb surface and the housing, and a second spacing angle (θ2) is formed between the second rear comb surface and the housing, wherein the comb portion is configured such that, when the comb is attached to the hair clipper, a spacing between the comb teeth and a housing of the hair clipper increases with distance away from the cutting element so as to form a substantially wedge-shaped hair debris-receiving space between the housing and the comb portion into which hair debris can flow, wherein the comb is an adjustable comb (200, 300, 300') for adjusting a cutting length of the hair clipper, and wherein a length of the first rear comb surface is equal to or greater than a cutting length range of the hair clipper, and wherein the comb comprises adjustment features defining a length adjustment direction of the comb, and wherein the length adjustment direction is substantially parallel to the first rear comb surface, such that a gap between the comb teeth and the cutting element in use is substantially constant for all cutting lengths in the cutting length range. a hair clipper having a housing and a cutting element; and a comb (200, 300, 300'), the comb (200, 300, 300') comprising: a comb portion (208, 308, 308') configured to be arranged forward of the cutting element of the hair clipper in a cutting movement direction (x) of the hair clipper, the comb portion comprising a plurality of comb teeth (216, 316) having slots (218, 318) formed there between for guiding hairs to be cut to the cutting element, wherein rear edges of the comb teeth, which face the housing of the hair clipper in use, define a first rear comb surface (324, 324') proximate the cutting element in use and a second planar rear comb surface (328, 328') ultimate the cutting element in use, and wherein the first spacing angle (θ1) is formed between the first rear comb surface and the housing, and a second spacing angle (θ2) is formed between the second rear comb surface and the housing, wherein the comb portion is configured such that, when the comb is attached to the hair clipper, a spacing between the comb teeth and a housing of the hair clipper increases with distance away from the cutting element so as to form a substantially wedge-shaped hair debris-receiving space between the housing and the comb portion into which hair debris can flow, wherein the comb is an adjustable comb (200, 300, 300') for adjusting a cutting length of the hair clipper, and wherein a length of the first rear comb surface is equal to or greater than a cutting length range of the hair clipper, and wherein the comb comprises adjustment features defining a length adjustment direction of the comb, and wherein the length adjustment direction is substantially parallel to the first rear comb surface, such that a gap between the comb teeth and the cutting element in use is substantially constant for all cutting lengths in the cutting length range.