Abstract. In this work we design hybrid continuous-discontinuous finite element spaces that permit discontinuities on non-matching element interfaces of non-conforming meshes. Then, we develop an equal-order stabilized finite element formulation for incompressible flows over these hybrid spaces, which combines the element interior stabilization of SUPGtype continuous Galerkin formulations and the jump stabilization of discontinuous Galerkin formulations. Optimal stability and convergence results are obtained. For the adaptive setting, we use an standard error estimator and marking strategy. Numerical experiments show the optimal accuracy of the hybrid algorithm both for uniformly and adaptively refined non-conforming meshes. The outcome of this work is a finite element formulation that can naturally be used on nonconforming meshes, as discontinuous Galerkin formulations, while keeping the much lower CPU cost of continuous Galerkin formulations.Key words. Incompressible flows, adaptive refinement, continuous-discontinuous Galerkin, equal-order interpolation, stabilization AMS subject classifications. 65N30, 35Q61, 65N121. Introduction. The dynamics of incompressible flows are governed by the incompressible Navier-Stokes equations, a set of nonlinear partial differential equations with a dissipative structure. Its numerical approximation is a challenging task. In the asymptotic regime of increasing Reynolds numbers the flow becomes chaotic (turbulent); mathematically, this is a singular limit with a coercivity loss [21]. On the other hand the system has a saddle-point (indefinite) structure, i.e. pressure stability relies on an inf-sup condition [37]. Galerkin finite element (FE) approximations that satisfy a discrete inf-sup condition can solve the second issue but the coercivity loss constrains one to capture all the spatial scales of the flow, i.e. to reduce the computational mesh size up to the Kolmogorov microscale, which is unaffordable in many realistic applications due to limited computational resources.Both issues can be solved by using residual-based FE stabilization techniques of SUPG-type [25,26,17,19]. These formulations make use of continuous FE spaces of functions, denoted as cG (continuous Galerkin) formulations onwards. The idea of these methods is to add to the Galerkin terms additional stabilizing terms that depend on the residual on the element interiors, keeping accuracy whereas improving stability. Stability does not depend on a discrete inf-sup condition anymore, and equal-order approximations can be used. Even for the Stokes problem, where the convective term does not appear, equal-order interpolation is very appealing in terms of implementation issues (simplicity of data-bases and matrix graphs) but also more efficient than inf-sup stable counterparts [31].Another approach to this problem is the use of non-conforming methods based on nodal discontinuous Galerkin (dG) techniques [16,22,34]. Convection stabilization is attained via a proper definition of the numerical fluxes [15,38]. Again, ...