Although more than 20 items in Scott's bibliography are singly-authored, he often has preferred to work in collaboration. His principal collaborators are listed alphabetically below, followed by synopses of the collaborations, indexed to his bibliography.
Aschbacher-Scott [35]
obtained a general theory of maximal subgroups of finite groups, reducing most questions to groups which were almost simple, and others to irreducible modules for the latter groups. Some of this had been proposed in the program Scott described in [29]. The latter paper adapted Dynkin's maximal subgroups program in Lie theory to finite group theory, and contained the often quoted Onan-Scott theorem, which described the types of maximal subgroups possible in the alternating groups. Actually, there were two theorems, and another gave an early version of the Aschbacher-Scott work. There was no collaboration between Onan and Scott, but both arrived at the 1979 Santa Cruz conference with similar results, and agreed to share credit. O'nan never published separately. "Same damn theorem" was Michael Onan's comment after seeing the manuscript Scott had brought with him. In spite of this vote of confidence, that version turned out to have some inaccuracies, and [35] includes corrections. For a revisiting of the theory of maximal subgroups in the case of finite groups of Lie type, and its several connections with linear representation theory, see [74].

Avrunin-Scott [33]
proved Carlson's conjecture that support and rank varieties defined the same sets, and established a Quillen stratification theory of cohomology of groups with nontrivial coefficients. Another main result was that the support variety of the tensor product of modules was the intersection of their respective support varieties. This is often inaccurately attributed to Carlson, who had only proved such a result for rank varieties for elementary groups. To work with cohomology varieties in the global case, Avrunin-Scott proved the (new) compatibility of support varieties with the inverse image of cohomological restriction. Another important method of proof in this paper was to regard the group algebra of an elementary abelian p-group as the restricted enveloping algebra of a commutative Lie p-algebra. The purpose was to get the right Hopf structure. This introduction of such algebras was the beginning of the support variety theory of Lie p-algebras later developed by Parshall-Friedlander.

Cline-Parshall-Scott (CPS) [9], [14], [17], [20], [22], [23], [24], [26], [34], [36], [38], [40], [41], [45], [49], [52], [55], [58], [59], [60], [66], [67], [75], [76].
Though multiply-authored papers are common in many scientific disciplines, most papers in mathematics have only one or two authors. CPS is by all accounts the longest continuously productive three-person collaboration in the history of mathematics. Their achievements include the proof [20] of Green's conjecture on exact induction and affine quotients, the demonstration [22] with van der Kallen of generic cohomology, the creation [45] of the theory of highest weight categories and quasihereditary algebras ([44], [47], [45]), the best purely algebraic reductions [55] of the Lusztig conjecture, and, recently, an expansion of many ideas of the defining characteristic theory of finite groups of Lie type into the nondefining arena, cf. [76]. Their older 1975 IHES paper [9] on 1-cohomology calculated many more results, more quickly than ever before, and is quoted in Andrew Wiles' proof of Fermat's Last Theorem (Annals of Math., 1995).

Cline-Parshall-Scott-van der Kallen [22]
See above.

Curtis-Scott
produced manuscripts in 1974 with the first generic block theory for Hecke algebras (including a complete defect 0 theory) and finite groups of Lie type in nondefining characteristics. There work was not published, but influenced work of Curtis's student R. Boyce and work of Hoefsmit-Scott described below.

Du-Scott [54], [57], [69] (see also Du-Parshall-Scott below)
developed in [57] some of the first integral theory of quantum enveloping algebras, and applied it to both the defining and nondefining characteristic representation theory of finite groups of Lie type. They discussed in the same framework conjectures of Lusztig and James (proving special cases), and introduced the notion of a generalized q-Schur algebra. Later, they introduced the q-Schur2 algebra, a decomposition-number preserving enlargement of an endomorphism algebra of type B important in the nondefining theory. This enlargement was quasihereditary in all cases, unlike the endomorphism algebra.

Du-Parshall-Scott [70], [71], [72]
undertook a broader enlargement project (see above) for nondefining characteristic endomorphism algebras in all root system types, using Kazhdan-Lusztig cells and the new CPS notion of a stratified algebra. As a by-product, they obtained in [72] [the most complete version (the full integral quantum case) of the Schur-Weyl double centralizer theorem].

Dlab-Scott [61]
edited a volume of invited papers from the 1993 Canadian Mathemtics Society conference on Representations of Algebras, especially devoted to finite dimensional algebras and Lie theory, and marking a new level of interaction between these areas.

Dunkl-Scott
is not so well known as a collaboration, but Dunkl and Scott were jointly responsible, cf. Scott's abstract [8], for the Krein condition, or rather, the realization that there was a positivity condition in finite permutation groups and combinatorics, perfectly analogous to a condition obtained in harmonic analysis by the Soviet mathematician M. G. Krein. An especially elementary proof, using observations by D. Higman on work of Schur, was presented by Scott in [12], who also presented further results. The impact of the Krein condition in combinatorics was substantial, and many (former) Soviets, especially the associates of Krein, were very grateful for the choice of name.

Feit-Lyndon-Scott [15]
gave a one-page elementary combinatorial proof of a result on permutations that had previously been obtained only through the theory of Riemann surfaces. Later, in his 1979 Annals paper, Scott [21] generalized the theory from permutations to matrices, incorporating the Riemann surface geometry into some inequalities based on algebraic 1-cohomology. This led, in the same paper of Scott, to a generalization, now widely applied, of a famous method of Brauer (the Brauer trick) for constructing nonobvious subgroups of finite groups.

Goldschmidt-Scott [25]
gave a counterexample to an open question of W. A. Manning, the leading expert in his day on permutation groups, of more than fifty years standing. The coauthors had exchanged ideas on previous occasions as well, and were office mates at Yale in 1970-71. Also, Goldschmidt had earlier been a graduate student while Scott was an instructor at the University of Chicago.

Hoefsmit-Scott
produced only a manuscript (1975), but it influenced later work of Scott's Ph.D. student, Leonard Jones, and Scott's postdoctoral student Jie Du. The manuscript contained, with some inaccuracies, the first effort at proving the Nakayama conjecture for Hecke algebras, as well as results on vertex and source theory, and a Mackey induction theory in the Hecke algebra case. Before he decided on a career in industry, Hoefsmit was Scott's postdoctoral student, following a well-known but never published Ph.D. dissertation at UBC, Vancouver.

Issacs-Scott [5]
proved some concrete results about blocks and restriction of characters. They also exchanged many ideas on permutation groups and subnormal subgroups as postdoctoral office mates at the University of Chicago in 1968-70.

Keller-Scott
produced only an abstract [2] from their common interests in permutation groups and representation, yet the collaboration was the major catalyst in Scott's decision to move from Yale to Virginia in 1971. Ed Cline (the 'C' in CPS above) had earlier been Keller's collaborator and colleague at the University of Minnesota, and Keller and Scott jointly sponsored Cline's visit in 1973-75 to the University of Virginia Mathematics Department.

Neumann-Scott [11], [18]
found several applications of character theory, especially modular theory, to finite permutation groups. They are unpublished, except for the abstract [18] by Scott. Nevertheless, the collaboration began Scott's long association with Oxford University, occasioning two visits there instigated by Neumann. In turn, Neumann met with Scott on two visits to the US, once as a short term visitor to the University Virginia. In addition, Neumann sent his Ph.D. student, Cheryl Praeger, to study as a postdoctoral student with Keller and Scott at Virginia, and his Ph.D. student, Jan Saxl, for a shorter visit.

Newhart-Scott [30]
are coauthors of a virtually complete handwritten manuscript applying the representation theory of permutation module endomorphism rings to combinatorial issues of interest in coding theory. Newhardt was the Ph.D. student of Scott's colleague, H. N. Ward, at the University of Virginia, and is currently employed by the National Security Agency.

O'Nan-Scott
See the discussion of Aschbacher-Scott above.

Parshall-Scott [28], [47], [63] (see also Cline-Parshall-Scott and Du-Parshall-Scott above, and Parshall-Scott-Wang below)
in their lectures (detailed, with additions, in the Moose notes [47]) at the 1989 Ottawa-Moosonee conference introduced, with considerable effect, the finite dimensional algebras community to the new notions of quasihereditary algebras and highest weight categories, born in the CPS research on algebraic group representations, cf. [41], [44], and [45]. In [63], combining methods of classical algebra and of etale cohomology, they produced a new proof (and, actually, the first into print) of the very strong Koszulity property for categories of perverse sheaves important in Lie representaion theory.

Parshall-Scott-Wang [77]
presented a complete revision of the theory of Borel subalgebras, and many new results, especially in the infinitesimal and quantum cases. In the process they gave replacements for an incorrect result in Scott's appendix [65], and alternative connections to Kazhdan-Lusztig theory, in the spirit of proposed results of S. Koenig.

Raymond-Scott [19],
using 3-cohomology, answered negatively (for higher dimensions) the question as to whether or not a well-known result of Nielsen in differential topology (on homotopy-periodic diffeomorphisms) generalized beyond 2-manifolds.

Roggenkamp-Scott [31], [32], [37], [39], [42], [50], [53],
in a ten-year collaboration produced unprecedented progress in understanding the famous finite group ring isomorphism problem (Graham Higman, Oxford thesis, 1940). Their main positive result [39] was the validity of the problem for finite nilpotent groups, and in an especially strong form for finite p-groups, which Higman and other experts had considered the worst case. However, in subsequent work, cf. [50], [56], Roggenkamp and Scott found a counterexample to a conjecture posed by Hans Zassenhaus, a stronger version of the problem, considered by Zassenhaus to be the key issue. Indeed, recently, M. Hertweck, partly building on the techniques of that counterexample, has now set forth details to a counterexample to the original problem of Higman. Hertweck is a Ph.D. student at U. Stuttgart of a former University of Virginia postdoctoral visitor, Wolfgang Kimmerle.