In this report we investigate the regularity of the solution to the fractional diffusion, advection, reaction equation on a bounded domain in R 1 . The analysis is performed in the weighted Sobolev spaces, H s (a,b) (I). Three different characterizations of H s (a,b) (I) are presented, together with needed embedding theorems for these spaces. The analysis shows that the regularity of the solution is bounded by the endpoint behavior of the solution, which is determined by the parameters α and r defining the fractional diffusion operator. Additionally, the analysis shows that for a sufficiently smooth right hand side function, the regularity of the solution to fractional diffusion reaction equation is lower than that of the fractional diffusion equation. Also, the regularity of the solution to fractional diffusion advection reaction equation is two orders lower than that of the fractional diffusion reaction equation.In this article we present the general regularity results for (1.3),(1.4), in appropriately weighted Sobolev spaces. The analysis establishes that the presence of a reaction term (i.e. c(x) = 0) limits the regularity of the solution, regardless of the smoothness of the right hand side function, f (x). This reduction in regularity is greater (by a factor of 2) when an advective term (i.e. b(x) = 0) appears in (1.3). This behavior of the solution is in sharp contrast to that for the integer order (α = 2) diffusion, advection, reaction equation. In that case, assuming b(x) and c(x) are sufficiently regular, for the right hand side function f ∈ H s (I) the solution lies in H s+2 (I).The results we present herein extend those in [13] for the fractional diffusion equation, and those in [22] for the fractional Laplacian equation with a constant advection and reaction term. The proofs given are significantly different that those used in [21,22].The analysis of (1.3),(1.4) is most appropriately performed in weighted Sobolev spaces (due to the singular behavior of the solution at the endpoints). There are different ways to define the weighted Sobolev spaces: (i) using interpolation (Section 3), (ii) using an appropriate basis (Section 4), (iii)