Marketing research is the systematic design, collection, analysis, and reporting of data relevant to a specific marketing situation. There are three main types of marketing research firms: syndicated firms that sell consumer and trade data, custom firms that conduct proprietary research for single clients, and specialty firms focused on a particular area. The marketing research process involves six steps: defining the problem and objectives, developing a research plan including data sources and sampling, collecting information, analyzing the data, presenting findings, and making decisions. Key considerations in developing a research plan include choosing primary or secondary data sources, research approaches like surveys and experiments, appropriate research instruments, sampling techniques, and contact methods.