We show that for each $$\gamma \in (0,2)$$
γ
∈
(
0
,
2
)
, there is a unique metric (i.e., distance function) associated with $$\gamma $$
γ
-Liouville quantum gravity (LQG). More precisely, we show that for the whole-plane Gaussian free field (GFF) h, there is a unique random metric $$D_h$$
D
h
associated with the Riemannian metric tensor “$$e^{\gamma h} (dx^2 + dy^2)$$
e
γ
h
(
d
x
2
+
d
y
2
)
” on $${\mathbb {C}}$$
C
which is characterized by a certain list of axioms: it is locally determined by h and it transforms appropriately when either adding a continuous function to h or applying a conformal automorphism of $$\mathbb {C}$$
C
(i.e., a complex affine transformation). Metrics associated with other variants of the GFF can be constructed using local absolute continuity. The $$\gamma $$
γ
-LQG metric can be constructed explicitly as the scaling limit of Liouville first passage percolation (LFPP), the random metric obtained by exponentiating a mollified version of the GFF. Earlier work by Ding et al. (Tightness of Liouville first passage percolation for $$\gamma \in (0,2)$$
γ
∈
(
0
,
2
)
, 2019. arXiv:1904.08021) showed that LFPP admits non-trivial subsequential limits. This paper shows that the subsequential limit is unique and satisfies our list of axioms. In the case when $$\gamma = \sqrt{8/3}$$
γ
=
8
/
3
, our metric coincides with the $$\sqrt{8/3}$$
8
/
3
-LQG metric constructed in previous work by Miller and Sheffield, which in turn is equivalent to the Brownian map for a certain variant of the GFF. For general $$\gamma \in (0,2)$$
γ
∈
(
0
,
2
)
, we conjecture that our metric is the Gromov–Hausdorff limit of appropriate weighted random planar map models, equipped with their graph distance. We include a substantial list of open problems.