The literature on horizontal tax interdependence pays limited attention to interactions in administrative policies, although they can play a large role in determining the amount of tax revenues collected. We investigate the incentives for sub-central tax authority cooperation in a decentralised context, with the aim of identifying the determinants of that cooperation. Our results are congruent with standard theory; in particular, the existence of reciprocity is essential for sharing tax information, but there is sluggishness in this process, which is partly the result of the short-sighted behaviour of tax authorities influenced by budget constraints. Hence, this is good news for the functioning of a decentralised tax administration as, in the medium to long run, the gains to be made from sharing tax information are achieved.