Space Group Preferences. There are strong space group preferences for experimentally observed crystal structures: over 80% of molecular crystals occupy 5 of the 230 threedimensional space groups. Having applied an approach in generating trial crystal structures that is unbiased in the how the 26 space groups included in our searches are sampled, we analyse the results of CSP to investigate space group preferences within the low energy structures on the set of crystal energy landscapes. We preface our analysis by emphasising that the space group frequencies presented in Figure are those for the CSP landscapes, i.e. only those of structures generated using an asymmetric unit containing a complete molecule (in these singlespecies systems, Z =1) and without detecting and assigning additional symmetry after the minimisation. In contrast, those of the observed crystal structures in the CSD are the full, maximal-symmetry space group (allowing fractions of molecules in the asymmetric unit, i.e . Z ≤ 1). Hence. the space groups enumerated for the CSP set can be thought of as "lower bounds" on the symmetry -higher-symmetry space groups may be assignable if the molecules present internal symmetry. The global lattice energy minimum for each molecule is the energetically preferred packing; the distribution of space groups among the global minima structures are highly consistent with the observed statistics -perhaps as expected, as CSP has been demonstrated in this work to often identify observed structures of these molecules as global minima. Space group frequencies are often explained by close packing arguments: the commonly observed space groups have combinations of symmetry elements that facilitate close packing of irregular shapes. Examining the space group distribution amongst the densest predicted crystal structure for each molecule gives a similar distribution to that from global energy minima; minimising energy and maximising density lead to similar space group preferences. However, there are differences after the three most popular space groups: the next few have almost equal frequencies among high density structures, suggesting that they are equally good at promoting close packing and that observed differences between these space groups relate to subtler influences of symmetry on lattice energy. Considering hypothetical structures higher on the CSP energy landscape (up to the usual energy limit of polymorphism, 7.2 kJ mol -1 , in the bottom right panel of Figure ), we see a further flattening of the distribution, and an overrepresentation of space group 15 (C 2/c) compared to global energy minima structures. These changes in distribution with energy, which we do not examine in deeper detail here, are only available from access to complete energy landscapes and are relevant in the discovery of high energy, metastable materials, which have sometimes been observed to have attractive properties.(24, 65) Thus, we feel that large datasets of CSP landscapes hold potential for generalising our understanding of symmetry preferences in molecular crystals.