We study the dynamics of dissipative spin lattices with power-law interactions, realized via fewlevel atoms driven by coherent laser-coupling and decoherence processes. Using Monte-Carlo simulations, we determine the phase diagram in the steady state and analyze the dynamics of its generation. As opposed to mean-field predictions and nearest-neighbour models there is no phase transition to long-range ordered phases for realistic interactions and resonant driving. However, for finite laser detunings, we demonstrate the emergence of crystalline order with a vanishing dissipative gap. Although the found steady states differ considerably from those of an equilibrium Ising magnet, the critical exponent of the revealed dissipative phase transition falls into the 2D Ising universality class. Two complementary schemes for an experimental implementation with cold Rydberg atoms are discussed. [5][6][7]. This requires sufficient time to remain adiabatic, which poses a challenging competition with the finite lifetime of the Rydberg states. Alternatively, this excited-state decay has been proposed as a natural means for dissipative state preparation [8]. The non-equilibrium physics of such driven open systems has recently attracted considerable interest [9][10][11][12], as their properties can differ dramatically from conventional equilibrium situations.Previous work considered lattices of effective spins, represented by an atomic ground and strongly interacting Rydberg state coupled by external laser driving and spontaneous decay [8,13,14]. The emergence of steady states with antiferromagnetic order was predicted on the basis of mean field theory assuming nearest-neighbour (NN) interactions [8]. It was later shown, however, that ordering in these systems is restricted to short length scales for all spatial lattice dimensions due to large singlesite fluctuations associated with a simple two-level driving scheme [14]. Simulations moreover showed that crystallization in 1D is precluded for other driving schemes [14], for which long-range order was predicted using mean field theory [15]. Hence, the possibility of long-range order in dissipative Rydberg lattices has thus far remained an open question.In this letter, we address this issue and show that longrange ordered antiferromagnetic phases can indeed be re- alized in dissipative Rydberg lattices when subject to appropriate coherent driving. However, fluctuations as well as the weak tail of the rapidly decaying interactions are both found to be essential for the physics of the dissipative phase transition. This stands in marked contrast to the equilibrium physics of the corresponding unitary systems, which often is well described by mean field models [16] and NN approximations [17]. The crystalline phase features a vanishing dissipative gap and strongly deviates from that of an equilibrium Ising magnet with finite arXiv:1404.1281v1 [cond-mat.quant-gas]