New brain imaging technology has emerged that might make it possible to read a person's thoughts directly from their brain activity. This novel approach is referred to as “brain reading” or the “decoding of mental states.” This article provides a general outline of the field and discusses its limitations, potential applications, and also certain ethical issues that brain reading raises. The measurement of brain activity and brain structure has made considerable progress in recent decades. The mapping from brain activity patterns to thoughts is learned for each specific subject using brute force statistical pattern recognition techniques. It discusses the degree to which polygraphy and brain-based lie detection can be manipulated by trained subjects. A future application of brain reading technology, “neuromarketing,” has received tremendous interest and there are repeated attempts to optimize marketing campaigns by adding brain-based sources of information.