There is little hope that the world will know secure software if wecannot make greater strides in the practice of formal methods:hardware and software devices with errors are routinely turned againsttheir users. The ProofCert proposal aims at building a foundationthat will allow a broad spectrum of formal methods---ranging fromautomatic model checkers to interactive theorem provers---to worktogether to establish formal properties of computer systems. Thisproject starts with a wonderful gift to us from decades of work bylogicians and proof theorist: their efforts on logic and proof hasgiven us a universally accepted means of communicating proofs betweenpeople and computer systems. Logic can be used to state desirablesecurity and correctness properties of software and hardware systemsand proofs are uncontroversial evidence that statements are, in fact,true. The current state-of-the-art of formal methods used inacademics and industry shows, however, that the notion of logic andproof is severely fractured: there is little or no communicationbetween any two such systems. Thus any efforts on computer systemcorrectness is needlessly repeated many time in the many differentsystems: sometimes this work is even redone when a given prover isupgraded. In ProofCert, we will build on the bedrock of decades ofresearch into logic and proof theory the notion of proof certificates.Such certificates will allow for a complete reshaping of the way thatformal methods are employed. Given the infrastructure and toolsenvisioned in this proposal, the world of formal methods will becomeas dynamic and responsive as the world of computer viruses and hackershas become.