We review the District Court’s denial of appellant’s motion under 9 U.S.C. § 3 1 for a stay of appellee’s breach of contract action. The action was clearly referable to arbitration under an agreement incorporated by reference into the contract between the parties. The only issue is whether the District Court erred in holding appellant “in default in proceeding with such arbitration.” 9 U.S.C. § 3. We think not.
The right to arbitration, like any other contract right, can be waived.2 A party waives his right to arbitrate when he actively participates in a lawsuit or takes other action inconsistent with that right.3 Once having waived the right to arbitrate, that party is necessarily “in default in proceeding with such arbitration.” 4
Before filing the present motion, appellant (1) moved for a transfer of venue to the Eastern District of Pennsylvania, (2) filed an answer to appellee’s complaint and a counterclaim, and (3) filed notice of depositions, took the deposition of an official of appellee, and procured the production of various records and documents. As the District Court stated:
[T]he litigation machinery had been substantially invoked and the parties were well into the preparation of a lawsuit by the time (some four months after the complaint was filed) an intention to arbitrate was communicated by the defendant to the plaintiff.
Appellant claims, however, that it did not learn of the arbitration clause until the above-mentioned production of documents. Absent fraud or concealment, which are not asserted here, appellant must be charged with knowledge of *514the terms of its own agreement. Otherwise, lack of diligence would become an excuse for the “dilatoriness or delay” which Congress meant to discourage.5
Affirmed.