It is shown that chaos analysis provides valuable tools to improve the design and operation of multiphase reactors, the most useful tools being the system's attractor and the Kolmogorov entropy. Applications of chaos analysis are based upon examining the attractor shape and/or on a characterization of the attractor by the Kolmogorov entropy. Examples are given by the characterization of regimes and regime transitions, scale up, control of the bubble pattern in the reactor to influence selectivity and conversion of chemical reactions, and the development of a tool to early detect agglomeration in fluidized beds.