The most popular ML models are brain-inspired models such as Neural Networks (NNs), including Convolutional Neural Networks (CNNs) and, more recently, Deep Neural Networks (DNNs). They are characterized by resembling the human brain, performing data processing by mimicking synapses using thousands of interconnected neurons in a network. In this growing environment, GPUs have become the de facto reference platform for the training and inference phases of CNNs and DNNs, due to their high processing parallelism and memory bandwidth. However, GPUs are power-hungry architectures. To enable the deployment of CNN and DNN applications on energy-constrained devices (e.g., IoT devices), industry and academic research have moved towards hardware accelerators. Following the evolution of neural networks from CNNs to DNNs, this monograph sheds light on the impact of this architectural shift and discusses hardware accelerator trends in terms of design, exploration, simulation, and frameworks developed in both academia and industry.