¶ 25 We agree with the circuit court's ruling that Urban Sites was estopped from bringing its cause of action based on the clear and unambiguous language of the 2005 agreement, which included an estoppel certificate, and we find that Urban Sites has not raised a genuine issue of material fact to survive summary judgment. ¶ 26 An estoppel certificate is a signed statement by a party, such as a landlord, certifying for another's benefit that certain facts pertaining to the tenancy are correct. K's Merchandise Mart, Inc. v. Northgate Ltd. Partnership, 359 Ill.App.3d 1137, 1143, 296 Ill.Dec. 612, 835 N.E.2d 965 (2005). Estoppel certificates are widely used in commercial real estate transactions and are important in preserving and enhancing the marketability of commercial property.

Swiatek v. Azran, 359 Ill.App.3d 500, 503, 296 Ill.Dec. 45, 834 N.E.2d 602, 604 (2005). The interpretation of a contract is a question of law, which we review de novo.K's Merchandise Mart, Inc. v. Northgate Ltd. Partnership, 359 Ill.App.3d 1137, 1142, 296 Ill.Dec. 612, 835 N.E.2d 965, 970 (2005). The primary objective when construing a contract is to determine and give effect to the intention of the parties at the time they entered into the contract. K's Merchandise Mart, Inc., 359 Ill.App.3d at 1142, 296 Ill.Dec. 612, 835 N.E.2d at 970.

Under Illinois law, "[t]he primary objective in construing a contract is to determine and give effect to the intention of the parties at the time they entered into the contract." K's Merch. Mart, Inc. v. Northgate Ltd. P'ship, 359 Ill.App.3d 1137, 296 Ill.Dec. 612, 835 N.E.2d 965, 970 (2005); see also Outboard Marine Corp. v. Liberty Mut. Ins. Co., 154 Ill.2d 90, 180 Ill.Dec. 691, 607 N.E.2d 1204, 1212 (1992). In reaching that objective, "[t]he language used in the contract generally is the best indication of the parties' intent."

¶ 25 We agree with the circuit court's ruling that Urban Sites was estopped from bringing its cause of action based on the clear and unambiguous language of the 2005 agreement, which included an estoppel certificate, and we find that Urban Sites has not raised a genuine issue of material fact to survive summary judgment. ¶ 26 An estoppel certificate is a signed statement by a party, such as a landlord, certifying for another's benefit that certain facts pertaining to the tenancy are correct. K's Merchandise Mart, Inc. v. Northgate Ltd. Partnership, 359 Ill. App. 3d 1137, 1143 (2005). Estoppel certificates are widely used in commercial real estate transactions and are important in preserving and enhancing the marketability of commercial property.

In an estoppel certificate, the signer is certifying the course of performance has not produced any defaults." K's Merchandise Mart v. Northgate Ltd. Partnership , 359 Ill.App.3d 1137, 1144 (II) (B), 296 Ill.Dec. 612, 835 N.E.2d 965 (2005). In this case, the BUC and the security guards had been passing through the traffic control gate on Regent's roadway system before the Association executed the Estoppel Certificate certifying that there were no defaults under the Easement.

In an estoppel certificate, the signer is certifying the course of performance has not produced any defaults." K's Merchandise Mart v. Northgate Ltd. Partnership , 359 Ill.App.3d 1137, 1144 (II) (B), 296 Ill.Dec. 612, 835 N.E.2d 965 (2005). In this case, the BUC and the security guards had been passing through the traffic control gate on Regent's roadway system before the Association executed the Estoppel Certificate certifying that there were no defaults under the Easement.

In Illinois, a written contract is presumed to include all material terms agreed upon by the parties, and evidence of prior negotiations is generally inadmissible. K's Merchandise Mart, Inc. v. Northgate Limited Partnership, 359 Ill.App.3d 1137, 1143, 296 Ill.Dec. 612, 835 N.E.2d 965, 971 (2005). This is especially true when the contract, as here, contains a complete-understanding clause, also referred to as an integration clause.

Sovereign Camp, etc. v. Heflin, 188 Ga. 234, 235(1), 3 S.E.2d 559 (1939). FN18. K's Merchandise Mart v. Northgate Ltd. Partnership, 359 Ill.App.3d 1137, 1144(II)(B), 296 Ill.Dec. 612, 835 N.E.2d 965 (2005). Further, in evaluating whether the Estoppel Certificate can preclude Fundus's claims, we are persuaded by the holding of the Appellate Court of Illinois that “[a] party who executes an Estoppel Certificate should not be allowed to raise claims of which it knew or should have known at the time the certificate was executed” and that “[a] party who executes an Estoppel Certificate that there are no defaults is under a duty to inquire and determine, insofar as reasonably possible, what claims exist.

An estoppel certificate can be enforceable even if the party signing it did so negligently. Because the law charged Fundus with the knowledge that a reasonable inspection would have uncovered, any dispute over the quality of Fundus's inspections does not give rise to an issue of material fact. Fundus expressly agreed in the assignment contract that appellees "shall have the right to rely" on the Estoppel Certificate, and Fundus cannot avoid that commitment by arguing circumstances that would otherwise give rise to an equitable estoppel. K's Merchandise Mart v. Northgate Ltd. Partnership, 359 Ill. App. 3d. 1137, 1144 (II) (B) ( 835 N.E.2d 965) (2005). Id.

Lakeview Management, Inc. v. Care Realty, LLC, No. 07-cv-303-SM, 2009 WL 903818, *19 (D.N.H. Mar. 30, 2009). It consists of a "`[a] signed statement by a party (such as a tenant or mortgagee) certifying for another's benefit that certain facts are correct. . . . A party's delivery of this statement estops that party from later claiming a different state of facts.'"Id. (quoting K's Merch. Mart, Inc. v. Northgate Ltd. P'ship, 359 Ill. App. 3d 1137, 1443, 835 N.E.2d 965, 971 (Ill. App. Ct. 2005). Therefore, here, Cinemaworld's representation in the Estoppel Certificate that "Rent ha[d] been paid through May 31, 2006," serves only to estop Cinemaworld from later claiming a different state of facts. Id.; see also Pl.'s Summ. J. Mem. Ex. K. The Estoppel Certificate was provided for Inland's benefit and may not now be used against it.