  Bipartite projections are used in a wide range of network contexts including
politics (bill co-sponsorship), genetics (gene co-expression), economics
(executive board co-membership), and innovation (patent co-authorship).
However, because bipartite projections are always weighted graphs, which are
inherently challenging to analyze and visualize, it is often useful to examine
the 'backbone', an unweighted subgraph containing only the most significant
edges. In this paper, we introduce the R package backbone for extracting the
backbone of weighted bipartite projections, and use bill sponsorship data from
the 114th session of the United States Senate to demonstrate its functionality.
