Helen Hall Jennings (September 20, 1905 – October 4, 1966) was an American social psychologist in the field of social networks in the early 20th century. She developed quantitative research methods used to study sociometry, a quantitative method for measuring social relationships. This work is cited as being the birth of social network analysis.

Jennings graduated from the New Jersey College for Women (now known as the Douglass Residential College at Rutgers University) in 1927 with a Bachelor of Letters degree.

Jennings pursued her graduate degree in psychology at Columbia University and specialized in empirical research design. While working in the lab of psychologist Gardner Murphy, she met Jacob L. Moreno. Through her knowledge of quantitative research methods and statistics, Jennings worked with Moreno to develop an empirical approach to social network research. Together they studied how "social relations affected psychological well-being” and “used quantitative methods for studying the structure of groups and the positions of individuals within groups."

Jennings and Moreno's research at Sing Sing and the New York Training School for Girls (also known as Hudson School for the Girls) "involved systematic data collection and analysis" and resulted in two published works: Application of the Group Method to Classification in 1932 and Who Shall Survive? A New Approach to the Problem of Human Interrelations in 1934. The approach of using quantitative data to study and measure relationships within groups of people resulted in the development of sociometry. Jennings and Moreno also became the first to use a stochastic network model (or, "chance sociogram", as they called it), predating the Erdős–Rényi model and the network model of Anatol Rapoport.

In 1931, Jennings received her Master of Arts degree from Columbia University. Her master's thesis was entitled "The nature of the pathetic." At that time she lived in Stelton, New Jersey. In 1943, Jennings completed her PhD thesis Leadership and Isolation: A Study of Personality in Interpersonal Relations, eventually published by Longman, Greens, and Company. Leadership and Isolation strove to examine how often-chosen leaders and isolates arise in a population. It was a continuation of analysis from the data collected at the New York Training School for Girls. Research participants were asked who they would like to work with and who they would like to live with. Eight months later, there was little change in the selected leaders and isolates.

Benjamin Karpman, a psychiatrist, describes the importance of Jennings's research in a review of the first edition of Leadership and Isolation for the Journal of Clinical Psychology. Karpman closes his review encouraging all psychiatrists to read Jennings’ book, stating, "it offers the most profound analysis of leadership and isolation in the social process this reviewer has discovered in the field of social psychology."

A second edition of Leadership and Isolation was published by Longman, Greens, and Company in 1950. Morris Janowitz, a founder of military sociology, reviewed the book for the American Journal of Sociology. In his review, Janowitz wrote that Leadership and Isolation "can be viewed as an ingenious empirical study which helped fashion sociometry as a research tool."

According to structural sociologist Linton C. Freeman, the empirical methods developed by Jennings and applied in Moreno's sociometry studies laid the groundwork for future social network research: