The two stages of the PCT process comprise of an international phase with an international application administered at the International Bureau, and a national phase when this is converted to national patent applications in the countries designated as potential states for patent protection in the initial application.
During the international phase, the designated International Searching Authority ISA conducts a patent search. The designated ISA is a Patent Office that has been authorised by WIPO to act as a Searching Authority e.g. the European Patent Office (EPO) or the United Kingdom Intellectual Property Office (UK IPO.
An International Search Report is provided around six months from filing to assist the applicant in deciding whether to proceed to the expensive national phase or to cut losses. The benefit of filing first nationally is the avoidance of unnecessary expenditure to reach this point. The International Bureau also publishes the patent specification.
The national phase of the PCT procedure involves the filing in each chosen designated country. This then becomes a bundle of opportunities to file applications. Accordingly this part can be expensive as official fees, and typically agents, in each country need to be paid. The national phase starts only if the applicant files applications in each designated Office of the country of choice just as a usual application would be filed. The applicant has sole responsibility and the consequences of failure to perform the act in due time are fatal in most designated States. In each such designated State the international application has the effect of a national (or regional if a regional office) application as from the filing date.
Next time, why you need to file a PCT and when.