Brain-computer interfaces (BCIs) aim to create a connection pathway for information exchange between the brain and devices with computing capabilities. The complexities of non-invasive BCIs and the implantation risks associated with invasive BCIs have confined these technologies to laboratory settings. A lack of foundational technologies of non-invasive and invasive BCIs, the signal processing challenges associated with BCIs, the key components of BCIs, and the compatibility of BCI software and hardware are challenges that need to be solved for BCI commercialization.