Results on Convergence in Norm of Exponential Product Formulas and Pointwise of the Corresponding Integral Kernels

For the last one and a half decades it has been known that the exponential product formula holds also {\it in norm} in nontrivial cases. In this note, we review the results on its convergence in norm as well as pointwise of the integral kernels in the case for Schr"odinger operators, with error bounds. Optimality of the error bounds is elaborated.