<p>Solid-state lithium (Li) metal batteries (SSLMBs), owning high energy density and superior safety, are regarded as promising future energy storage technologies. However, Li anodes in this system continuously degrade during battery storage and cycling. This process leads to the formation and accumulation of inactive Li (<i>i.e.</i>, “dead Li” that has lost its ion/electron contact), ultimately resulting in poor lifespans of SSLMBs. Though some progress has been made in liquid systems, there is still a lack of a systematic summary regarding the generation and alleviation of inactive Li in SSLMBs. In this review, we first analyze the formation of inactive Li in SSLMBs, which primarily stems from the thermodynamic instability of Li and slow Li-ion transport kinetics. Subsequently, strategies for migrating, inhibiting, or reutilizing inactive Li trapped within the electrolyte and at the Li/electrolyte interface are summarized and discussed. Finally, the advancement in diagnosing inactive Li has been reviewed, offering a valuable recognition for improving the longevity and safety of SSLMBs. By providing such key insights into inactive Li chemistry, this review paves the way for the practical implementation of SSLMBs.</p>