diff --git a/include/ro-crate.hpp b/include/ro-crate.hpp
index 63018bd..2d6f5d0 100644
--- a/include/ro-crate.hpp
+++ b/include/ro-crate.hpp
@@ -107,6 +107,17 @@ namespace rocrate {
       throw std::invalid_argument("Cannot set '@id' property directly. "
                                   "Use ROCrate::addEntity to assign an ID.");
 
+    // Check property is not duplicate - ignore if so
+    auto it = properties_->find(property);
+    if (it != properties_->end()) {
+      for (const auto& existingValue : it->second) {
+        if (existingValue.value == value && existingValue.type == valueType) {
+          // Duplicate found, ignore
+          return;
+        }
+      }
+    }
+
     // Add the value to the property in the properties map
     (*properties_)[property].push_back({value, valueType});
   }
@@ -194,6 +205,15 @@ namespace rocrate {
      */
     void writeOut(const std::string& path);
 
+    /**
+      * Reads an RO-Crate from a JSON file at the specified path and populates
+      * the current RO-Crate instance with the entities and context from the file.
+      *
+      * @param path The file path from which to read the RO-Crate JSON.
+      * @throw std::runtime_error if there is an error reading from the file or parsing the JSON.
+     */
+    void readIn(const std::string& path);
+
   private:
     nlohmann::json serializeEntity(
         const std::string& id,
@@ -208,6 +228,11 @@ namespace rocrate {
         const PropertyValue& value
     ) const;
 
+    void updateProperties(
+      Entity& entity,
+      const nlohmann::json& jsonEntity
+    );
+
     EntityRegister entities_;
     std::map<std::string, std::string> context_;
   };
@@ -301,6 +326,90 @@ namespace rocrate {
     outFile << outCrate.dump(4); // Pretty print with 4 spaces indentation
   }
 
+  inline void ROCrate::readIn(const std::string& path) {
+    // Read the JSON representation of the RO-Crate from a file
+    std::ifstream inFile(path);
+    if (!inFile) 
+      throw std::runtime_error("Failed to open file for reading: " + path);
+
+    // Check if valid JSON
+    nlohmann::json inCrate;
+    try {
+      inFile >> inCrate;
+    } catch (const nlohmann::json::parse_error& e) {
+      throw std::runtime_error("Failed to parse JSON from file: " + path + ". Error: " + e.what());
+    }
+
+    // Validate the RO-Crate structure
+    if (!inCrate.contains("@context") || !inCrate.contains("@graph")) {
+      throw std::runtime_error("Invalid RO-Crate structure in file: " + path);
+    }
+
+    // Upsert the context entries from the JSON representation into the RO-Crate
+    if (inCrate["@context"].is_array()) {
+      for (const auto& contextEntry : inCrate["@context"]) {
+        if (contextEntry.is_object()) {
+          for (const auto& [key, value] : contextEntry.items()) {
+            addContext(key, value.get<std::string>());
+          }
+        }
+      }
+    }
+
+    // Iterate over the entities in the JSON representation and add them to the RO-Crate
+    for (const auto& entityJson : inCrate["@graph"]) {
+      // Validate that the entity has an '@id' field
+      if (!entityJson.contains("@id")) {
+        throw std::runtime_error("Entity in RO-Crate JSON is missing '@id' field.");
+      }
+      std::string entityId = entityJson["@id"].get<std::string>();
+
+      // Get the entity type
+      if (!entityJson.contains("@type")) {
+        throw std::runtime_error("Entity in RO-Crate JSON is missing '@type' field.");
+      }
+      std::string entityType = entityJson["@type"].get<std::string>();
+
+      // Try getting the entity from the register, if it exists, otherwise create a new one
+      Entity entity({"Thing"}); // Default type, will be overridden if entity exists
+      try {
+        // Existing entity
+        entity = getEntity(entityId);
+        updateProperties(entity, entityJson);
+      } catch (const std::runtime_error&) {
+        // Entity does not exist, create a new one
+        entity = Entity({entityType});
+        updateProperties(entity, entityJson);
+        addEntity(entityId, entity);
+      }
+    }
+  }
+
+  inline void ROCrate::updateProperties(Entity& entity, const nlohmann::json& entityJson) {
+      // Iterate over the properties of the entity and add them to the Entity object
+      for (const auto& [property, value] : entityJson.items()) {
+        if (property == "@id") {
+          continue; // Skip the @id property
+        }
+
+        // Handle the property value based on its type (array, object, or literal)
+        if (value.is_array()) {
+          // If array, iterate over the items and add them to the Entity object
+          for (const auto& item : value) {
+            if (item.is_object() && item.contains("@id")) {
+              entity.set(property, item["@id"].get<std::string>(), ValueType::Reference);
+            } else {
+              entity.set(property, item.get<std::string>(), ValueType::Literal);
+            }
+          }
+        } else if (value.is_object() && value.contains("@id")) {
+          entity.set(property, value["@id"].get<std::string>(), ValueType::Reference);
+        } else {
+          entity.set(property, value.get<std::string>(), ValueType::Literal);
+        }
+      }
+  }
+
   inline nlohmann::json ROCrate::serializePropertyValue(
       const PropertyValue& value
   ) const {
diff --git a/tests/integration.cpp b/tests/integration.cpp
index 6080384..9b7a599 100644
--- a/tests/integration.cpp
+++ b/tests/integration.cpp
@@ -192,3 +192,25 @@ TEST_CASE("RO-Crate which focuses on multiple Contextual Entities", "[integratio
     outputPath
   );
 }
+
+TEST_CASE("ReadIn RO-Crate roundtrips successfully", "[integration]")
+{
+  // Create a new RO-Crate object
+  ROCrate crate;
+
+  // Read in the RO-Crate from a file (into the crate object)
+  const std::string inputPath =
+    std::string(TEST_SOURCE_DIR) + "/tests/fixtures/minimal-example-of-ro-crate.json";
+  crate.readIn(inputPath);
+
+  // Write back out
+  const std::string outputPath =
+    std::string(TEST_SOURCE_DIR) + "/ro-crate-metadata.json";
+  crate.writeOut(outputPath);
+
+  // Assert that the input and output files are equal by ID
+  REQUIRE_RO_CRATE_FILE_EQUAL_BY_ID(
+    inputPath,
+    outputPath
+  );
+}
diff --git a/tests/unit.cpp b/tests/unit.cpp
index ca94674..587ec36 100644
--- a/tests/unit.cpp
+++ b/tests/unit.cpp
@@ -63,6 +63,15 @@ TEST_CASE("Rejects empty link property names", "[unit]") {
     );
 }
 
+TEST_CASE("Ignore duplicate key-value pairs", "[unit]") {
+    Entity entity({"Thing"});
+
+    REQUIRE_NOTHROW(entity.set("name", "value"));
+    REQUIRE_NOTHROW(entity.set("name", "value")); // Should not throw, but also not add a duplicate
+
+    SUCCEED("No exceptions thrown, can't currently assert on entity values as they are not exposed in the API");
+}
+
 TEST_CASE("Ensure failure if entity is linked before being assigned an ID", "[unit]") {
     // Create the person, but do not add to a crate (so no @id yet)
     Entity alice({"Person"});
@@ -156,3 +165,23 @@ TEST_CASE("Add entity rejects entities with duplicate IDs", "[unit]") {
   aliceDuplicate.set("name", "Alice Duplicate");
   REQUIRE_THROWS_AS(crate.addEntity("#alice", aliceDuplicate), std::runtime_error);
 }
+
+TEST_CASE("Write out RO-Crate to JSON-LD without throwing", "[unit]") {
+  rocrate::ROCrate crate;
+
+  Entity alice({"Person"});
+  alice.set("name", "Alice");
+  crate.addEntity("#alice", alice);
+
+  REQUIRE_NOTHROW(crate.writeOut("output/ro-crate-metadata.json"));
+}
+
+TEST_CASE("Read in RO-Crate from JSON-LD without throwing", "[unit]") {
+  rocrate::ROCrate crate;
+
+  REQUIRE_NOTHROW(
+    crate.readIn(
+      std::string(TEST_SOURCE_DIR) + "/tests/fixtures/minimal-example-of-ro-crate.json"
+    )
+  );
+}