This thesis describes and evaluates two new interferometric distance measurement methods based upon the well known method of Frequency Scanning Interferometry (FSI). These new methods are known as Dynamic FSI and Cascaded FSI. Dynamic FSI addresses the two problems, commonly seen in previous FSI implementa- tions, of not being able to measure a moving target and having a slow measurement rate. This method measures stationary and moving targets equally well, and can determine the distance to the target at all times during the measurement, in contrast to previous methods, which obtain only a single measured length from a measurement process which can take up to a second to make. Cascaded FSI was developed with the aim of increasing the accuracy and precision of FSI. This method allows for measurements with precision equal to that of displacement interferometry, and also provides a way of measuring length relative to the frequencies of atomic absorption lines, which are inherently more stable length references than a physical length artefact.