We have developed some general ways of studying nonleptonic decays and CP‐nonvariance: the Quark Diagram Scheme, which has been very useful in making predictions, and in analyzing data and model‐calculations. For the quark‐mixing matrix of Cabibbo‐Kobayashi‐Maskawa (CKM), we have constructed, inspired by the Wolfenstein parametrization and taking full advantage of the theoretical and experimental situation, a suitable parametrization which (partly coincides with Maiani’s) is now adopted by the Particle Data Book; we also found the universal decay‐amplitude CP‐noninvariance factorXCPand introduced the use of the unitary triangles of the CKM matrix, which are now the standard language in analyzing CP‐noninvariance and nonleptonic weak decays.