  The van de Waals interaction between two graphene sheets is studied at finite
temperatures. Graphene's thermal length $(\xi_T = \hbar v / k_B T)$ controls
the force versus distance $(z)$ as a crossover from the zero temperature
results for $z\ll \xi_T$, to a linear-in-temperature, universal regime for
$z\gg \xi_T$. The large separation regime is shown to be a consequence of the
classical behavior of graphene's plasmons at finite temperature. Retardation
effects are largely irrelevant, both in the zero and finite temperature
regimes. Thermal effects should be noticeable in the van de Waals interaction
already for distances of tens of nanometers at room temperature.
