pH measurements have been performed in the chemistry from the very beginning, although before 1909 - for obvious reasons (see pH definition to find out why) - they were not called this way. However, fact that solution must be acidic or basic, and that its acidity can be checked with natural indicators (like litmus or red cabbage juice) was known much earlier.
At present pH measurements are part of routine tests done to check potable water quality, soil usability for different plants, water quality in aquaristics, they are done to control industrial processes, in wine-making and beer-making, to check milk quality, to check cosmetics - not to mention all labs throughout the world where pH measurements are performed many times a day to control reactions and analysis conditions.
pH can be measured in several ways, of which two are widely used. One - simple and often enough precise - is a use of pH strips (pH papers). Second, more costly and more demanding in terms of procedure that have to be used, but giving much more precise results - is a potentiometric method with usage of pH electrodes and pH meters. Colorimetric (spectroscopic) methods have never gained much popularity, although they are occasionally used in places where pH electrodes can't be immersed in the solution and the pH stripes can't be used.