Accelerators now play a crucial role in computing systems. With the emergence of a new wave of academic and industrial high-level synthesis (HLS) tools, FPGA-based accelerators now are more accessible to software programmers. However, there are several burdens placed upon the programmers to design a high-performance accelerator when using FPGA, such as different memory and parallel programming models. Therefore, a high-level structured design approach targeting accelerator is essential. This approach advances software programming techniques to utilise FPGAs efficiently. This book explains the concept of accelerator design using current high-level synthesis tools and techniques. It describes different types of regular and irregular accelerator patterns as a structured building block for FPGA implementation. The cutting-edge programming models based on C/C++ and OpenCL are used to explain standard computation and memory patterns through many examples and case studies. In short, this book - offers theory and practice of HLS parallel programming techniques for FPGA - describes parallel patterns for regular and irregular algorithms - contains detailed examples in C/C++ and OpenCL for HLS - represents the efficiency of FPGA accelerators through several case studies in scientific computation and machine learning areas