Master Oscillator Power Amplifiers (MOPA) are laser systems that utilize a seed and pump amplification system to boost the output power of high-quality lower power seeding signals. MOPAs can generate high gain while avoiding many of the nonlinearities that negatively affect resonance-based lasers that are known to feature higher internal intensities. Additionally, MOPAs provide an easy alternative to the construction of novel laser technologies for higher output power as they can be easily combined with existing laser sources to amplify their output power. This thesis outlines the design of an ytterbium-doped fiber laser (YDFL), featuring a MOPA architecture. The YDFL is constructed to amplify a continuous wave single mode signal, at 1064nm, from 366mW to 16.4W while maintaining high spectral purity and beam quality. This laser is being developed with the intention to seed a subsequent MOPA YDFL for amplification to 1.5kW, for use in following thermal blooming experiments. As a result, the laser being developed in this work must have high spectral purity, centered near 1064nm, and a narrow linewidth, less than 0.25nm. Methods for limiting instabilities within the MOPA amplification stages are developed and the final seed laser emission quality is demonstrated in this work.