PIL DIFFERS significantly from other forms of litigation as regards a person's legal right to file a suit. Traditionally, only an aggrieved party had the locus standi to sue for judicial redress. In PIL, the court has broadened and liberalised the concept of locus standi to read: If the fundamental rights of an individual or a class of persons are violated and if, for reasons of poverty or disability, the aggrieved party cannot approach the court, any public-spirited individual or institution, acting in good faith, can move the Supreme Court and the high courts for judicial redress in public interest, claiming an infringement of fundamental rights under Articles 32 and 226 of the Constitution, respectively. Writs challenging the working of government agencies and policies are also admitted as PIL.

PIL evolved in the US in the 1950s with the judiciary committing itself to the task of social reconstruction, when the courts required schools in southern American states to end racial segregation. In India, PIL gained momentum in the early 1980s. After the Emergency, there was much concern for social justice. The period also saw the emergence of the legal aid movement, with which Justices P N Bhagwati and V R Krishna Iyer were closely associated.

With the liberalising of the concept of locus standi, environmental violations were brought to the notice of courts along with cases of human rights violation. The courts expanded the boundaries of the fundamental right to life and personal liberty guaranteed under Article 21 to include environmental protection.

In a landmark judgement by the Andhra Pradesh High Court in the Damodhar Rao versus S O Municipal Corporation case, where an attempt by some government departments to build residential houses in an area reserved for parks was challenged, the court held "the enjoyment of life and its attainment and fulfillment guaranteed by Article 21 of the Constitution embraces the protection and preservation of nature's gifts without which life cannot be enjoyed. The slow poisoning caused by environmental pollution and spoilation should also be regarded as a violation of Articles 21."