The synthesis of complex molecules such as those used in pharmaceuticals depends heavily on the ability to rapidly and efficiently construct carbon-carbon bonds. Over the past decades, olefin metathesis has become a key tool for such a process. Olefin metathesis has been used widely in drug discovery and is now moving into process chemistry. A number of pharmaceutical agents that are made possible by the metathesis reaction have proceeded through Phase II trials and a number are now entering into Phase III. Although the olefin metathesis reaction has been known for a number of decades, it has only become useful in organic synthesis with the discovery of highly active and stable catalysts that are tolerant of most functional groups and are easily used by organic chemists. The modification of ligands on the basic ruthenium-based metathesis complexes has resulted in highly efficient catalysts that are used in a wide array of applications, from pharmaceutical synthesis to the construction of high end composites. Each advance in catalyst efficiency and selectivity has opened a variety of new applications. One of the final deficiencies in catalyst design has been the lack of control of double bond geometry. In most cases, the reactions produce a majority of the more stable E geometric isomer. During the last granting period, major breakthroughs have been made in the design of catalyst that will produce Z-olefins in high yields from simple terminal olefins. These catalysts open many new applications. During the next granting period, efforts will be made to increase their efficiency and selectivity, and to develop applications that exploit their capabilities. Building on the lessons from the discovery of a Z-selective catalyst, new systems will be designed that will be focused on the synthesis of purely E-olefins. The results from the next granting period will further enhance the utility of the powerfl olefin metathesis reaction in the synthesis of new pharmaceuticals and bioactive molecules.