All the three models allow for a deviation from the ideal octahedra of the cubic phase, with the R3m showing two groups of Fig. Fit of the X-ray PDF data at 300 K from 2.0 to 5.0 Å for MASnBr3 against the orthorhombic model. three Sn-Br distance equal to each other, the I4cm having three pairs of equal distances, whereas the Pmc21 induces a further distortion with only two distances equal to each other. The peak related to the Br-Br correlation is broader than the one in the iodide counterparts, as already reported in previous characterizations , and was attributed to a low rigidity of the octahedra. A similar description can be applied to FASnBr3 (Figure in ESI), where the spread of distances, both for the Sn-Br and Br-Br correlation, is even more pronounced, and an orthorhombic distortion is necessary to describe the crystal structure. In fact, the broadening of the first two peaks is even larger. Fits with the cubic, rhombohedral and tetragonal models are very poor, whereas an orthorhombic distortion better reproduces the experimental trends (Figure -12 in ESI). The models selected to describe the local structure for the RT data are depicted in the first line of Figure . When moving to the low temperature data, peaks get sharper, but we observe a similar trend of increasing distortion by increasing the size of the A cation and the hardness of the anion (Figure ). MASnI3 (Panel A in Figure ) shows quite sharp peaks for both the Sn-Br and Br-Br correlation, suggesting the presence of close to ideal octahedra. Fits with the I4/mcm, the same space group of the average structure at 80 K, R3m, and I4cm all give better results than the Pm3¯m (Figures in ESI), with a slightly worse agreement with the I4/mcm, suggesting that a small degree of offcentering of the B cation is present also at low temperature. When moving to FASnI3 (Panel B in Figure ), the first peak clearly shows asymmetry. The models tested with the room temperature data, Pm3¯m, R3m, and I4cm, were also applied to the data at 80 K, but did not yield a good agreement (Figure in ESI). Interestingly, the R3m model, which allows only for the displacement of the B cation but not for the tilting of the octahedra, is not able to reproduce the asymmetry of the Sn-Br correlations. When the tilting is included, for example with the I4cm model, the correlation is better described, suggesting that octahedral tilting might play an important role in the local structure of FASnI3. To further explore this hypothesis, we tested different tilts. The model P4/mbm, which corresponds to the tilt a 0 a 0 c + in Glazer notation , does not provide a good fit to the data, whereas the I4/mcm and Pnma models, a 0 a 0 c -and a + b -b -tilts respectively, show a better agreement (Figures and in ESI). All of the three tilts involve a rotation on the z-axis parallel to the fourfold axis, the first tilt system gives rise to layers of octahedra with exactly the same relative orientation, whereas the other two to layers with opposite relative orientations. This type of tilting seems to provide a better fit to the experimental trends. The likelihood of an orthorhombic distortion is also supported by the fact that the average structure at 80 K has Pnma space group , and that the local structure of other MHPs, such as MAPbBr3 8 and MAPbCl3 10 , was described with this symmetry. The bromide compounds, in analogy with the room temperature data, have some distinctive features with respect to the iodide ones. The peak related to the Br-Br correlation is broader and the signal due to the Sn-Br correlation is clearly split in two peaks: one sharper and one asymmetric, in contrast with MASnI3 and FASnI3 that only show broadening and asymmetry (Panels A and B in Figure ). The cubic, tetragonal, and rhombohedral models are not able to reproduce the experimental trend, in particular the second peak related to Sn-Br distances (Figure in ESI). An orthorhombic model with the Pmc21 shows a better agreement (Figure ): the first sharp peak can be attributed to three Sn-Br distances close to 2.73 Å, and the second asymmetric peak to three longer distances. As expected from the trends highlighted so far, the distortion from the ideal cubic symmetry is larger in FASnBr3 and also in this case the cubic, tetragonal and rhombohedral models fail in reproducing the experimental trends, whereas an orthorhombic distortion provides a better fit (Figure -15 in ESI). This systematic characterization of the local structure of tin halide perovskite by total scattering methods and PDF analysis, shed light on the extension and nature of local distortions as a function of composition and temperature. Larger displacements are observed when increasing the cation size, i.e. from MA to FA, and the hardness of the anion, i.e. from Br to I. . Furthermore, a certain degree of orthorhombicity was found to be always present in the investigated compositions at any temperature and crystal symmetry, possibly due to the hydrogen bonding with the organic group strongly affecting the local structure . This description perfectly fits the local structure of lead halide perovskites and is in good agreement with present results, in particular at low temperature and for the bromide compounds, displaying larger distortion. On the other hand, at room and higher temperature the local structure of tin iodide compounds seems to be more affected by off-centering of B site cation due to the larger activity of the lone pair with respect to lead analogs. To summarize, a clear trend of increasing local distortion has been evidenced in tin halide perovskite as a function of organic cation, halide and temperature. The present results are of key importance in clarifying the structureproperty correlation of lead-free MHPs which are the most appealing materials to overcome the toxicity issues of lead-based systems for photovoltaic devices.