This chapter gives a brief summary of the reported discoveries, confirmation, and nuclear properties of the claimed and confirmed transactinide elements through the year 2004. However, the primary emphasis is on the chemical properties - experimental, theoretical, and predicted - of the transactinides and a comparison of measured properties with theoretical predictions. The experimental studies of chemical properties are especially challenging because of the low production rates and the short half-lives and the need for very special facilities and the use of atom-at-a-time chemistry. The discovery of a new element must furnish evidence that its atomic number is different from those of all the currently known elements and first claims to discovery often lacked such positive identification. As a result, there were uncertainties and controversies over priority of discovery, nuclear and chemical properties, and assignment of names. The first positive identification of the atomic number of all these elements was accomplished using ‘physical' rather than chemical techniques.