Diagnostic development is an important and vital part of the fusion program. There is close coupling between the physics needs for measurements and the diagnostic development that receives funding. This paper gives brief technical descriptions of ongoing developments in a few areas currently receiving attention. These areas include Te diagnostics, j(R) diagnostics applicable to new regimes, and diagnostics to probe edge and core turbulence. The underlying physics motivation and enabling technologies involved in these developments are also mentioned. A brief status of diagnostic work in support of a burning plasma experiment (BPX) is also described, since this effort may become more significant worldwide. Several diagnostic R&D topics, identified as crucial for a BPX, are discussed.