Empirical research is research using empirical evidence. It is also a way of gaining knowledge by means of direct and indirect observation or experience. Empiricism values some research more than other kinds. Empirical evidence (the record of one's direct observations or experiences) can be analyzed quantitatively or qualitatively. Quantifying the evidence or making sense of it in qualitative form, a researcher can answer empirical questions, which should be clearly defined and answerable with the evidence collected (usually called data). Research design varies by field and by the question being investigated. Many researchers combine qualitative and quantitative forms of analysis to better answer questions that cannot be studied in laboratory settings, particularly in the social sciences and in education.

In some fields, quantitative research may begin with a research question (e.g., "Does listening to vocal music during the learning of a word list have an effect on later memory for these words?") which is tested through experimentation. Usually, the researcher has a certain theory regarding the topic under investigation. Based on this theory, statements or hypotheses will be proposed (e.g., "Listening to vocal music has a negative effect on learning a word list."). From these hypotheses, predictions about specific events are derived (e.g., "People who study a word list while listening to vocal music will remember fewer words on a later memory test than people who study a word list in silence."). These predictions can then be tested with a suitable experiment. Depending on the outcomes of the experiment, the theory on which the hypotheses and predictions were based will be supported or not, or may need to be modified and then subjected to further testing.

The experimental method has evolved over the ages, with many scientists contributing to its foundation and development. In ancient times, Greek philosophers, such as Aristotle, relied on observation and rational inference in their studies. Aristotle, for example, rejected exclusive reliance on logical deduction, emphasizing the importance of observation in understanding nature.

During the Middle Ages, Muslim scientists significantly advanced the experimental method. Jabir ibn Hayyan, known as the father of chemistry, introduced experimental methodology into chemistry and developed chemical processes such as crystallization, calcination, and distillation. He also discovered important acids like sulfuric and nitric acid, expanding the possibilities of chemical experiments. The famous optics scientist Alhazen (Ibn al-Haytham) was among the first to rely on experimentation in studying light and vision. In his book Book of Optics, he employed a scientific method based on observation, experimentation, and mathematical proof, making him a pioneer of the modern scientific method.

These scientific approaches were transmitted to Europe through translations, influencing the development of modern scientific methodology. European scientists, such as Francis Bacon, were inspired by the works of Muslim scholars in refining the experimental method. The researcher Robert Briffault, in his book Making of Humanity, states:

"It was under their successors at Oxford School (that is, successors to the Muslims of Spain) that Roger Bacon learned Arabic and Arabic Sciences. Neither Roger Bacon nor later namesake has any title to be credited with having introduced the experimental method. Roger Bacon was no more than one of apostles of Muslim Science and Method to Christian Europe".

The term empirical was originally used to refer to certain ancient Greek practitioners of medicine who rejected adherence to the dogmatic doctrines of the day, preferring instead to rely on the observation of phenomena as perceived in experience. Later empiricism referred to a theory of knowledge in philosophy which adheres to the principle that knowledge arises from experience and evidence gathered specifically using the senses. In scientific use, the term empirical refers to the gathering of data using only evidence that is observable by the senses or in some cases using calibrated scientific instruments. What early philosophers described as empiricist and empirical research have in common is the dependence on observable data to formulate and test theories and come to conclusions.

The researcher attempts to describe accurately the interaction between the instrument (or the human senses) and the entity being observed. If instrumentation is involved, the researcher is expected to calibrate his/her instrument by applying it to known standard objects and documenting the results before applying it to unknown objects. In other words, it describes the research that has not taken place before and their results.