Humans in which humans may control machines with their brains. Understanding current new technologies, such as Brain-Computer Interface, can help to ensure that successful solutions become a part of daily life. The latest advancement in Human-Computer Interaction is the Brain-Computer Interface (BCI) (HCI). BCI allows for either directly generated commands between external software applications and the human brain (active BCI) or communication between individuals and machines, resulting in a seamless and advantageous user experience (passive BCI). With over 100 billion nerve cells, the human brain is responsible for numerous sophisticated executive activities such as reasoning, task planning, and thinking processing. As a result, the brain generates a significant amount of neural activity, which can be used as input in a variety of BCI applications. This chapter provides a thorough examination of the current state-of-the-art of a complete BCI system. First, a brief introduction of BCI systems based on electroencephalograms (EEGs) is provided. Second, a large variety of well-known BCI applications are examined in terms of electrophysiological control signals, feature extraction, classification techniques, and performance evaluation metrics. Finally, the problems with modern BCI systems are explored, and potential remedies to the problems are suggested.