We consider a multi-resolution representation based on a decomposition of the field domain into nested tetrahedral cells generated by recursive tetrahedron bisection, that we call a Hierarchy of Tetrahedra (HT) We describe our implementation of an HT, and discuss how to extract conforming meshes from an HT so as to avoid discontinuities in the approximation of the associated scalar field. We describe algorithms for selective refinement, which either extract a variable-resolution mesh from scratch through a depth-first, or through a priority-based traversal technique, or which locally refine and coarsen a previously-extracted adaptive mesh through an incremental approach. We show experimental results in connection with a set of basic queries for performing analysis and visualization of a volume data set at different levels of detail.