High-order methods for conservation laws can be highly efficient if their stability is ensured. A suitable means mimicking estimates of the continuous level is provided by summation-by-parts (SBP) operators and the weak enforcement of boundary conditions. Recently, there has been an increasing interest in generalised SBP operators both in the finite difference and the discontinuous Galerkin spectral element framework. However, if generalised SBP operators are used, the treatment of the boundaries becomes more difficult since some properties of the continuous level are no longer mimicked discretely -interpolating the product of two functions will in general result in a value different from the product of the interpolations. Thus, desired properties such as conservation and stability are more difficult to obtain. Here, new formulations are proposed, allowing the creation of discretisations using general SBP operators that are both conservative and stable. Thus, several shortcomings that might be attributed to generalised SBP operators are overcome (cf.There are classical finite difference operators that can be interpreted in an analytical setting similar to the one described above [19]. However, in general -to the authors knowledge -it is not known whether finite difference SBP operators correspond to an analytical basis. Nevertheless, the basic requirement of the SBP property (4) can be enhanced by accuracy conditions in order to get a useful definition of (numerical) SBP operators, cf. [11,59].Definition 1. Using a numerical representation u = (u 0 , . . . , u p ) T of a function u in a nodal basis, the operators D , R , M , and B described above form a qth order SBP discretisation, if 1. the derivative matrix D is exact for polynomials of degree q, 2. the mass / norm matrix M is symmetric and positive definite, 3. the SBP property (4) is fulfilled, and