A better understanding of the factors that control the solutionphase morphology of semiconducting polymers can potentially help to systematically improve device performance, as this morphology has been correlated with thin-film structure, and with device performance. For the high-performance semiconducting polymer poly[N,N'-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene) (P(NDI2OD-T2)), also known as N2200, the formation of large rod-like aggregates has been observed experimentally in poor solvents such as toluene and xylene, and has been shown to be associated with increased electron mobility in films deposited from these solutions. In these poor solvents, P(NDI2OD-T2) (M n = 31.2 kDa, polydispersity = 2.1) was shown, via UV-vis spectroscopy, to aggregate extensively. However, counter to a conventional understanding on solution-phase aggregation of flexible polymers, which predicts R g to decrease with decreasing solvent quality, these aggregates were shown, using smallangle X-ray scattering (SAXS), to have a radius of gyration R g larger than that of a single chain, suggestive of the formation of extended multi-chain structures that are not predicted by existing theories. This result contrasts with conclusions from a previous study of P(NDI2OD-T2) which, based on the lack of dependence on polymer concentration of the spectral shift in poor solvents and analytical centrifugation measurements, suggested that aggregation behaviour in toluene is a single-chain process caused by chain collapse and folding. Notably, these experiments were conducted at a much lower concentration than the SAXS measurements (up to 1 g/L, versus 5 g/L for the SAXS experiments ), as well as using significantly longer chains (118, 181, or 1105 kDa in ref. 12 versus 31 kDa in ref. 10), which may explain the reported discrepancy. Indeed, multi-chain aggregation has been observed for other semiconducting polymers such as MEH-PPV, PffBT4T-2DT, D-DPP3T-EH, and PffBT4T-2OD, with concentration-and molecular-weight-dependent effects observed but not fully explained.