The main focus of the thesis is on issues concerning production of knowledge. It is a common observation that knowledge activities have a tendency to agglomerate as well as to spill over in space. In order to incorporate geographical proximity, the thesis applies an accessibility approach in which actual travel time distances between locations are used to discount spatial knowledge spillovers. The thesis consists of three individual essays and a joint introduction. The first essay explores to what extent accessibility to R&D conducted at universities and companies can explain the number of patent applications in Swedish municipalities. The second essay analyses the relationship between knowledge accessibility and regional export performance. The knowledge resources used are R&D efforts and university educated labour. Since the distributions of the dependent variables are skewed with a few influential outliers, the estimations are conducted with quantile regressions. The empirical findings indicate that accessibility to university R&D has minor effects on patent production and export performance in Sweden. However, the other used inputs, i.e. accessibility to company R&D and accessibility to university educated labour, are of greater importance. The results also show that knowledge flows transcend municipal borders but that they tend to be bounded within functional regions. The third essay investigates how the inclusion of accessibility variables, i.e. spatially lagged explanatory variables, affects the extent of spatial autocorrelation. The basic proposition is that the inclusion of inputs external to the spatial observation as separate variables reveals spatial dependencies via the parameter estimates. This is confirmed by Monte Carlo simulations. The Monte Carlo Simulations also indicate that problems with spatial autocorrelation and biased parameter estimates are reduced.