diff --git a/src/cooling.h b/src/cooling.h
new file mode 100644
index 0000000000000000000000000000000000000000..4c4694c86b07e587aa4f6e9a48ff046d0b180f34
--- /dev/null
+++ b/src/cooling.h
@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+#ifndef SWIFT_COOLING_H
+#define SWIFT_COOLING_H
+
+/**
+ * @file src/cooling.h
+ * @brief Branches between the different cooling functions.
+ */
+
+/* Config parameters. */
+#include "../config.h"
+
+/* Local headers. */
+#include "const.h"
+
+/* Import the right cooling definition */
+#if defined(COOLING_CONST_COOLING)
+#include "./cooling/const/cooling.h"
+#elif defined(COOLING_CREASEY_COOLING)
+#include "./cooling/creasey/cooling.h"
+#elif defined(COOLING_GRACKLE_COOLING)
+#include "./cooling/grackle/cooling.h"
+#else
+#error "Invalid choice of cooling function."
+#endif
+
+#endif /* SWIFT_COOLING_H */
diff --git a/src/cooling/creasey/cooling.c b/src/cooling/creasey/cooling.c
new file mode 100644
index 0000000000000000000000000000000000000000..4ee03aa9bcbe0fb616fe90c1844da98a3c1ccf79
--- /dev/null
+++ b/src/cooling/creasey/cooling.c
@@ -0,0 +1,175 @@
+
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2016 Tom Theuns (tom.theuns@durham.ac.uk)
+ * Matthieu Schaller (matthieu.schaller@durham.ac.uk)
+ * Richard Bower (r.g.bower@durham.ac.uk)
+ * Stefan Arridge (stefan.arridge@durham.ac.uk)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+
+/* Config parameters. */
+#include "../config.h"
+
+/* This object's header. */
+#include "adiabatic_index.h"
+#include "cooling.h"
+#include "hydro.h"
+
+/**
+ * @brief Initialises the cooling properties in the internal system
+ * of units.
+ *
+ * @param parameter_file The parsed parameter file
+ * @param us The current internal system of units
+ * @param cooling The cooling properties to initialize
+ */
+void cooling_init(const struct swift_params* parameter_file,
+ struct UnitSystem* us,
+ const struct phys_const* const phys_const,
+ struct cooling_data* cooling) {
+
+#ifdef CONST_COOLING
+ cooling->const_cooling.lambda =
+ parser_get_param_double(parameter_file, "Cooling:lambda");
+ cooling->const_cooling.min_energy =
+ parser_get_param_double(parameter_file, "Cooling:min_energy");
+ cooling->const_cooling.cooling_tstep_mult =
+ parser_get_param_double(parameter_file, "Cooling:cooling_tstep_mult");
+#endif /* CONST_COOLING */
+
+#ifdef CREASEY_COOLING
+ cooling->creasey_cooling.lambda =
+ parser_get_param_double(parameter_file, "CreaseyCooling:Lambda");
+ cooling->creasey_cooling.min_temperature = parser_get_param_double(
+ parameter_file, "CreaseyCooling:minimum_temperature");
+ cooling->creasey_cooling.mean_molecular_weight = parser_get_param_double(
+ parameter_file, "CreaseyCooling:mean_molecular_weight");
+ cooling->creasey_cooling.hydrogen_mass_abundance = parser_get_param_double(
+ parameter_file, "CreaseyCooling:hydrogen_mass_abundance");
+ cooling->creasey_cooling.cooling_tstep_mult = parser_get_param_double(
+ parameter_file, "CreaseyCooling:cooling_tstep_mult");
+
+ /*convert minimum temperature into minimum internal energy*/
+ float u_floor =
+ phys_const->const_boltzmann_k * cooling->creasey_cooling.min_temperature /
+ (hydro_gamma_minus_one * cooling->creasey_cooling.mean_molecular_weight *
+ phys_const->const_proton_mass);
+ float u_floor_cgs =
+ u_floor * units_cgs_conversion_factor(us, UNIT_CONV_ENERGY_PER_UNIT_MASS);
+
+ cooling->creasey_cooling.min_internal_energy = u_floor;
+ cooling->creasey_cooling.min_internal_energy_cgs = u_floor_cgs;
+#endif /* CREASEY_COOLING */
+}
+
+/**
+ * @brief Prints the properties of the cooling model to stdout.
+ *
+ * @param cooling The cooling properties.
+ */
+void cooling_print(const struct cooling_data* cooling) {
+
+#ifdef CONST_COOLING
+ message(
+ "Cooling properties are (lambda, min_energy, tstep multiplier) %g %g %g ",
+ cooling->const_cooling.lambda, cooling->const_cooling.min_energy,
+ cooling->const_cooling.cooling_tstep_mult);
+#endif /* CONST_COOLING */
+
+#ifdef CREASEY_COOLING
+ message(
+ "Cooling properties for Creasey cooling are (lambda, min_temperature, "
+ "hydrogen_mass_abundance, mean_molecular_weight, tstep multiplier) %g %g "
+ "%g %g %g",
+ cooling->creasey_cooling.lambda, cooling->creasey_cooling.min_temperature,
+ cooling->creasey_cooling.hydrogen_mass_abundance,
+ cooling->creasey_cooling.mean_molecular_weight,
+ cooling->creasey_cooling.cooling_tstep_mult);
+#endif /* CREASEY_COOLING */
+}
+
+void update_entropy(const struct phys_const* const phys_const,
+ const struct UnitSystem* us,
+ const struct cooling_data* cooling, struct part* p,
+ float dt) {
+
+ /*updates the entropy of a particle after integrating the cooling equation*/
+ float u_old;
+ float u_new;
+ float new_entropy;
+ // float old_entropy = p->entropy;
+ float rho = p->rho;
+
+ // u_old = old_entropy/(GAMMA_MINUS1) * pow(rho,GAMMA_MINUS1);
+ u_old =
+ hydro_get_internal_energy(p, 0); // dt = 0 because using current entropy
+ u_new = calculate_new_thermal_energy(u_old, rho, dt, cooling, phys_const, us);
+ new_entropy = u_new * pow_minus_gamma_minus_one(rho) * hydro_gamma_minus_one;
+ p->entropy = new_entropy;
+}
+
+/*This function integrates the cooling equation, given the initial
+ thermal energy, density and the timestep dt. Returns the final internal
+ energy*/
+
+float calculate_new_thermal_energy(float u_old, float rho, float dt,
+ const struct cooling_data* cooling,
+ const struct phys_const* const phys_const,
+ const struct UnitSystem* us) {
+#ifdef CONST_COOLING
+ /*du/dt = -lambda, independent of density*/
+ float du_dt = -cooling->const_cooling.lambda;
+ float u_floor = cooling->const_cooling.min_energy;
+ float u_new;
+ if (u_old - du_dt * dt > u_floor) {
+ u_new = u_old + du_dt * dt;
+ } else {
+ u_new = u_floor;
+ }
+#endif /*CONST_COOLING*/
+
+#ifdef CREASEY_COOLING
+ /* rho*du/dt = -lambda*n_H^2 */
+ float u_new;
+ float X_H = cooling->creasey_cooling.hydrogen_mass_abundance;
+ float lambda_cgs = cooling->creasey_cooling.lambda; // this is always in cgs
+ float u_floor_cgs = cooling->creasey_cooling.min_internal_energy_cgs;
+
+ /*convert from internal code units to cgs*/
+ float dt_cgs = dt * units_cgs_conversion_factor(us, UNIT_CONV_TIME);
+ float rho_cgs = rho * units_cgs_conversion_factor(us, UNIT_CONV_DENSITY);
+ float m_p_cgs = phys_const->const_proton_mass *
+ units_cgs_conversion_factor(us, UNIT_CONV_MASS);
+ float n_H_cgs = X_H * rho_cgs / m_p_cgs;
+ float u_old_cgs =
+ u_old * units_cgs_conversion_factor(us, UNIT_CONV_ENERGY_PER_UNIT_MASS);
+ float du_dt_cgs = -lambda_cgs * n_H_cgs * n_H_cgs / rho_cgs;
+ float u_new_cgs;
+
+ if (u_old_cgs + du_dt_cgs * dt_cgs > u_floor_cgs) {
+ u_new_cgs = u_old_cgs + du_dt_cgs * dt_cgs;
+ } else {
+ u_new_cgs = u_floor_cgs;
+ }
+ /*convert back to internal code units when returning new internal energy*/
+
+ u_new = u_new_cgs /
+ units_cgs_conversion_factor(us, UNIT_CONV_ENERGY_PER_UNIT_MASS);
+
+#endif /*CREASEY_COOLING*/
+ return u_new;
+}
diff --git a/src/cooling/creasey/cooling.h b/src/cooling/creasey/cooling.h
new file mode 100644
index 0000000000000000000000000000000000000000..62ecbd75d92d687c1f56124d6c0802ef6a1b6851
--- /dev/null
+++ b/src/cooling/creasey/cooling.h
@@ -0,0 +1,100 @@
+/*******************************************************************************
+ * This file is part of SWIFT.
+ * Copyright (c) 2016 Tom Theuns (tom.theuns@durham.ac.uk)
+ * Matthieu Schaller (matthieu.schaller@durham.ac.uk)
+ * Richard Bower (r.g.bower@durham.ac.uk)
+ * Stefan Arridge (stefan.arridge@durham.ac.uk)
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ ******************************************************************************/
+
+#ifndef SWIFT_CREASEY_COOLING_H
+#define SWIFT_CREASEY_COOLING_H
+
+/* Some standard headers. */
+#include <math.h>
+
+/* Local includes. */
+#include "const.h"
+#include "error.h"
+#include "hydro.h"
+#include "parser.h"
+#include "part.h"
+#include "physical_constants.h"
+#include "units.h"
+
+/* Cooling Properties */
+struct cooling_data {
+
+#ifdef CONST_COOLING
+ struct {
+ float lambda;
+ float min_energy;
+ float cooling_tstep_mult;
+ } const_cooling;
+#endif
+
+#ifdef CREASEY_COOLING
+ struct {
+ float lambda;
+ float min_temperature;
+ float hydrogen_mass_abundance;
+ float mean_molecular_weight;
+ float min_internal_energy;
+ float min_internal_energy_cgs;
+ float cooling_tstep_mult;
+ } creasey_cooling;
+#endif
+};
+
+/* Include Cooling */
+#ifdef CONST_COOLING
+
+/**
+ * @brief Computes the time-step due to cooling
+ *
+ * @param cooling The #cooling_data used in the run.
+ * @param phys_const The physical constants in internal units.
+ * @param Pointer to the particle data.
+ */
+__attribute__((always_inline)) INLINE static double cooling_timestep(
+ const struct cooling_data* cooling,
+ const struct phys_const* const phys_const, const struct part* const p) {
+
+ const double cooling_rate = cooling->const_cooling.lambda;
+ const double internal_energy =
+ hydro_get_internal_energy(p, 0); // dt = 0 because using current entropy
+ return cooling->const_cooling.cooling_tstep_mult * internal_energy /
+ cooling_rate;
+}
+
+#endif /* CONST_COOLING */
+
+/* Now, some generic functions, defined in the source file */
+void cooling_init(const struct swift_params* parameter_file,
+ struct UnitSystem* us,
+ const struct phys_const* const phys_const,
+ struct cooling_data* cooling);
+
+void cooling_print(const struct cooling_data* cooling);
+void update_entropy(const struct phys_const* const phys_const,
+ const struct UnitSystem* us,
+ const struct cooling_data* cooling, struct part* p,
+ float dt);
+float calculate_new_thermal_energy(float u_old, float rho, float dt,
+ const struct cooling_data* cooling,
+ const struct phys_const* const phys_const,
+ const struct UnitSystem* us);
+#endif /* SWIFT_CREASEY_COOLING_H */