We develop a collective field theory for fractional quantum Hall (FQH) states. We show that in the leading approximation for a large number of particles, the properties of Laughlin states are captured by a Gaussian free field theory with a background charge. Gradient corrections to the Gaussian field theory arise from the covariant ultraviolet regularization of the theory, which produces the gravitational anomaly. These corrections are described by a theory closely related to the Liouville theory of quantum gravity. The field theory simplifies the computation of correlation functions in FQH states and makes manifest the effect of quantum anomalies.PACS numbers: 73.43. Cd, 73.43.Lp, Introduction Since the work of Laughlin [1], a common approach to analyzing the physics of the fractional quantum Hall effect (FQHE) starts with a trial ground state wave function for N electrons. Despite its success, this approach is an impractical framework for studying the collective behavior of a large number of electrons ( N ∼ 10 6 , in samples exhibiting the QHE). As a result, some subtle properties of QHE states, such as the gravitational anomaly [2-10], were computed only recently.The effects of quantum anomalies are essential in the physics of the QHE. Although anomalies originate at short distances on the order of the magnetic length, they control the large-scale properties of the state, such as transport. It was recently shown in [10] that, like the Hall conductance, transport coefficients determined by the gravitational anomaly are expected to be quantized on QH plateaus. For this reason it is important to formulate the theory of QH effect in a fashion which makes the quantum anomalies manifest. The field theory approach seems the most appropriate for this purpose.In this paper, we develop a field theory for Laughlin states. This approach naturally captures universal features of the QHE, and emphasizes geometric aspects of QH-states. We demonstrate how the field theory encompasses recent developments in the field [2-10] and obtain some properties of quasi-hole excitations. Preliminary treatment of this approach appears in [3].The field theory framework uncovers a connection between the QHE and random geometry, specifically 2D Liouville quantum gravity. Since its introduction, the Laughlin wave function has been a practical model wave function mainly because of the plasma analogy. This analogy to a 2D statistical mechanical system allowed the most salient features of the state -uniform density and fractional quasi-hole charge -to be easily captured by a saddle point approach to the partition function of the equivalent plasma.Every analysis to date has stopped at the saddle point. as a result subtle features of the theory such as the gravitational anomaly were missed. We show how the Laughlin wave function maps to a full quantum field theory. This approach allows to go beyond the saddle point and