Most human organs consist of solid tissues. Most human disorders occur in solid tissues. No two cells are equivalent in native solid tissues as single cells widely vary in their biochemistry, specialization, and location. Yet, the fundamental limitations of solid-tissue processing and analysis have made it challenging to access the richness of molecular information in single cells of animal and human solid tissues. We have eliminated a set of limitations of solid-tissue processing and analysis. In this thesis, I first describe a new method for sampling single cells in live solid tissues. This method preserves the molecules of all molecular classes and thus fulfills the precondition for multiplexing within and across molecular classes. I then describe new analytical methods and strategies for massively multiplex analysis within and across molecular classes in each sampled single cell. Standard curves, the basis of analytical methods, can be constructed in all measurements and signals can be mapped to the corresponding quantities. Proof of principle experiments are presented. These methods will enable the quantification of the molecular mechanism of each sampled single cell in solid tissues by analytically measuring tens of proteins, transcripts and/or metabolites at once. By performing these measurements in human solid-tissue biopsies, we will be able to define a new category of diagnostic tests, to personalize single-cell pharmacology and to rapidly identify mechanistic biomarkers and drug targets.