Technical Abstract: 1 Accurate identification of all life stages is essential to detect and successfully control and contain the spread of invasive forest pests. Despite its economic importance as an invasive species, the pre–imaginal stages of the wood–boring beetle, Agrilus planipennis, remain poorly described. 2 This study provides the most detailed description of the immature stages of A. planipennis to date and illustrates suites of larval characters useful in distinguishing among Agrilus species and instars. 3 Segregation of Agrilus larvae into two groups, the A. viridis and the A. ater groups was supported. 4 Agrilus planipennis larvae are more similar to larvae of species in the A. viridis group than to species in the A. ater group. 5 The retention of A. planipennis in the subgenus Uragrilus was not supported based on larval characters. 6 Agrilus planipennis larvae possess the following combination of character states, including the first 5 states, which are unique: 1, bell–shaped abdominal segments; 2, segment 10 setation sparse; 3, narrow, cylindrical anal terminal processes with numerous ledges appearing after instar I; 4, zig–zag posterior contour of the microsetal area on prementum; 5, space between the anterior margin of prementum and posterior border of microsetal area is equal to approximately 2/5 of the distance from anterior margin to the bases of the apical setae; 6, anal terminal processes with 2–3 excretory ducts; 7, microdentate area surrounding pronotal and prosternal grooves without smooth area; 8, pronotal groove posteriorly bifurcating; 9, prosternal groove entire; 10, labrum glabrous with margin not produced anterolaterally; 11, microspinulae concentrated subapically on the mala and internal surface of the stipes and cardo; 12, mandibles deltoid with well–defined apical teeth and large penicillum; 13, antennal segment 2 quadrate.