The Department of Environment and Natural Resources (DENR) had its beginnings in the old Department of Agriculture and Natural Resources (DANR). In May 1974, the DANR was split into two departments through P.D. 461 in recognition that natural resources and agriculture are broad and differing concerns. As such, the Department of Natural Resources (DNR) was mandated to ensure the conservation, optimum, utilization, and programmed exploitation of the country's natural wealth including the aquatic resources. With the shift to a parliamentary form of government in 1978, the DNR became the Ministry of Natural Resources (MNR). In 1984, by virtue of Executive Order No. 697, the management of fisheries sector through the Bureau of Fisheries and Aquatic Resources (BFAR), was transferred from the MNR to the Minitry of Agriculture.

The events of February 1986 brought social awareness among the Filipino people that altered the character of the Ministry of Natural Resources (MNR). The creation of DENR under Executive Order No. 131 on January 30, 1987 and the issuance of Executive Order 192 on June 10, 1987 better known as the "Reorganization Act of the Department of Environment and Natural Resources" brought a radical shift in the Department's structure and functions. Pursuant to the Executive Order, the DENR became the primary government agency responsible for the conservation, development and optimum use of the natural resources as well as the protection and development of a sustainable environmental management system for the benefit and welfare of the Filipino people.

The approval of the Philippine Mining Act or R.A. 7945 and implementation of DAO No. 97-11 brought changes to the structure of the Regional Office, relieving Mines and Geo-Sciences Sector from the Region and authorizing this Sector to perform line function.
Changes brought by the passing and approval of the Clean Air Act or R.A. 8749 mandating the Region's Environment Sector to operate as line Bureau. To date, an interim structure has been organized to cater to the needs and demands of constituents in the Mainland Provinces and Island Provinces.

Implementation of DAO 99-14 dated May 05, 1999 provided for the redefinition of functions and realignment of administrative units in the Regional and Field Offices. DAO 99-52 dated December 15, 1999 prescribed a detailed defenition of functions for the realigned regional divisions that finally spelled-out the development and reforms initiatives.

Recognizing the need to accelerate the sectoral and economic development through improved delivery of services in the provinces and cities of Region IV, Executive Order 103 was approved on May 17, 2002, creating Region IV-A and Region IV-B, while Aurora province was transferred under the territorial and administrative jurisdiction of Region III. Region IV-A comprising the provinces ofCAvite, LAguna, BAtangas, Rizal and QueZON with ten (10) cities was named as CALABARZONwhile the Region IV-B composed of the island provinces of MIndoro Occidental and Oriental,MArinduque, ROmblon and PAlawan provinces with two (2) cities was dubbed the MIMAROPARegion.

The Regional Office of DENR-MIMAROPA is presently situated at the L&S Bldg, Roxas Boulevard, Malate, Manila although there are plans to be relocated to the MIMAROPA regional center in Calapan City, Oriental Mindoro.

DENR-MIMAROPA has five (5) Provincial Environment and Natural Resources Offices (PENROs) located in Mamburao, Occidental Mindoro; Calapan City, Oriental Mindoro; Boac, Marinduque; Puerto Princesa City, Palawan; and Odiongan, Romblon.

Its Community Environment and Natural Resources Offices (CENROs) are found in Mamburao, Sablayan and San Jose (Occidental Mindoro); Calapan City, Socorro and Roxas (Oriental Mindoro); Boac (Marinduque); Puerto Princesa City, Roxas, Taytay, Coron, Narra, Quezon and Brooke’s Point (Palawan); and Odiongan (Romblon).
Organizational Chart ( I don’t know how to copy image, pls. refer to Region 4b)