Immigration into New Zealand is currently at an all-time high (Statistics New Zealand, 2024) and the New Zealand housing market is considered one of the least affordable in the OECD (Fitchett & Jacob, 2022). Motivated by these factors, this thesis estimates the impact of immigration on rental costs in New Zealand. Using a customised extension of the New Zealand public release census data from 1991 to 2018, I perform a fixed effects analysis to estimate the impact of immigration relative to domestic migration or overall population growth on local average rental costs in New Zealand at either a Ward or finer Area Unit level. I also use a two stage least squares regression with an instrumental variable for immigration to control for potential endogeneity. My analysis suggests that immigration has a positive and significant impact on average rental costs in New Zealand relative to other forms of local population increase. These results are robust to several different measures of immigration and hold when robustness checks are carried out. From heterogeneity analysis, the effect is stronger in urban areas or when the largest New Zealand regions are examined.