Intense, ultrashort laser pulses are required for the study of many nonlinear optical effects and are of utmost relevance for various applications from ultrafast X-ray radiography in medicine up to remote sensing of the atmosphere. Increasing theirintensity while interacting with matter eventually leads to the generation of laser-induced plasma. This plasma has fascinating optical properties such as a negative refractive index contribution proportional to the free electron density or the lack of a damage threshold, giving the prospect of a multitude of new applications based on the manipulation of light with plasma. The realization of such plasma-based applications requires a precise knowledge of its properties and temporal evolution, as the plasma remains for much longer than its generation event. A method to generate and investigate ultrashort laser pulses as well as laser-induced plasma is femtosecond filamentation. It represents the formation of an intense self-guided light channel in a medium for distances much longer than the Rayleigh range of the same beam focused in vacuum. It is formed by a dynamic balance of Kerr-induced self-focusing and plasma-induced defocusing. In this thesis, it is demonstrated that femtosecond filamentation can be employed as a tool to investigate the temporal evolution of laser-induced plasma. The study is realized in various atomic and molecular gas atmospheres via measuring the temporal evolution of the enhancement of third harmonic radiation generated by a femtosecond filament which is intercepted by a laser-induced plasma spot. Significant differences for the lifetime of the plasma in atomic and molecular gas atmospheres are found. Further, a novel method for the complete spatio-temporal characterization of a femtosecond filament along its length is presented. It is based on controlled filament termination at various positions along its length in combination with spatio-temporal pulse characterization and numerical backpropagation of the filament pulses to the termination point. The capabilities of the method are illustrated by revealing complex spatio-temporal dynamics and couplings during filament propagation.