In this paper, members of NERA’s Global Transfer Pricing Practice discuss the newly issued Cost Sharing Regulations, which replace the 1995 regulations for determining taxable income in connection with Cost Sharing Arrangements (CSAs). The new regulations include specific instructions regarding the calculation of buy-in payments, or “Platform Contribution Transactions.” The new regulations also define how Intangible Development Cost shares related to ongoing development activities should be determined. The authors note that there are new documentation and accounting requirements that are more stringent than before and require taxpayers with ongoing CSAs to act soon in conforming their CSAs to the new guidance. This paper reviews these requirements and describes the annual update process.