Although the Treaty of Waitangi itself does not have any force in the law of modern day New Zealand, the actions of the people involved in the treaty still influence people today. This is because the "principles of the treaty" have become a part of New Zealand law and have affected the way in which New Zealand deals with its Maori citizens.
For example, the New Zealand government has written into law the idea that the Maori tribes should have some level of control over their resources. The law also allows for people to claim redress for violations of the treaty. Because these principles have been written into law, the actions of the people involved in the treaty continue to influence New Zealanders today. These have led, for example, to significant Maori involvement in the fishing and forestry industries. On the negative side, it has led to some amount of conflict between those who wish to preserve the treaty and those who wish to remove its principles from the law.