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Bacteria often live in multicellular communities known as biofilms. Unlike their planktonic counterparts, bacteria in biofilms are encapsulated in an extracellular matrix, a complex mixture of macromolecules (including DNA). We use biophotonics and soft matter approaches to quantitatively explore interactions of cells with the extracellular polymeric matrix in the biofilms. Our group utilizes holographic laser trapping to manipulate positions and orientations of hundreds of cells in 3D, measure cell-matrix interaction forces, the strength of binding of bacteria to surfaces, and many-body interactions between bacteria during the so-called "quorum sensing" and at later stages of the biofilm formation. This study will advance quantitative understanding of structural organization in bacterial biofilms and is of both biomedical and technological importance.