diff --git a/src/testdatagen/formatters/csv_formatter.py b/src/testdatagen/formatters/csv_formatter.py
new file mode 100644
index 0000000..b92abe2
--- /dev/null
+++ b/src/testdatagen/formatters/csv_formatter.py
@@ -0,0 +1,129 @@
+"""CSV output formatter."""
+
+import csv
+import io
+import json
+from typing import Any, Dict, List
+
+
+class CSVFormatter:
+    """Formatter that outputs data in CSV format."""
+
+    def __init__(self, delimiter: str = ",", quotechar: str = '"'):
+        """Initialize the CSV formatter.
+
+        Args:
+            delimiter: Column delimiter character
+            quotechar: Quote character for fields containing delimiters
+        """
+        self.delimiter = delimiter
+        self.quotechar = quotechar
+
+    def format(self, records: List[Dict[str, Any]]) -> str:
+        """Format records as CSV string.
+
+        Args:
+            records: List of data records to format
+
+        Returns:
+            CSV-formatted string
+        """
+        if not records:
+            return ""
+
+        all_keys = self._extract_all_keys(records)
+
+        output = io.StringIO()
+        writer = csv.DictWriter(
+            output,
+            fieldnames=all_keys,
+            delimiter=self.delimiter,
+            quotechar=self.quotechar,
+            quoting=csv.QUOTE_MINIMAL,
+            extrasaction='ignore'
+        )
+
+        writer.writeheader()
+
+        for record in records:
+            flattened = self._flatten_record(record)
+            writer.writerow(flattened)
+
+        return output.getvalue()
+
+    def _extract_all_keys(self, records: List[Dict[str, Any]]) -> List[str]:
+        """Extract all unique keys from records.
+
+        Args:
+            records: List of records
+
+        Returns:
+            List of all unique keys in order of first appearance
+        """
+        seen = set()
+        result = []
+
+        for record in records:
+            flattened = self._flatten_keys(record)
+            for key in flattened:
+                if key not in seen:
+                    seen.add(key)
+                    result.append(key)
+
+        return result
+
+    def _flatten_keys(self, obj: Any, parent_key: str = "") -> List[str]:
+        """Flatten nested structure and extract all keys.
+
+        Args:
+            obj: Object to extract keys from
+            parent_key: Prefix for nested keys
+
+        Returns:
+            List of flattened keys
+        """
+        if not isinstance(obj, dict):
+            return [parent_key] if parent_key else []
+
+        keys = []
+        for key, value in obj.items():
+            new_key = f"{parent_key}.{key}" if parent_key else key
+            if isinstance(value, dict):
+                keys.extend(self._flatten_keys(value, new_key))
+            elif isinstance(value, list) and value and isinstance(value[0], dict):
+                for i, item in enumerate(value):
+                    keys.extend(self._flatten_keys(item, f"{new_key}[{i}]"))
+            else:
+                keys.append(new_key)
+
+        return keys
+
+    def _flatten_record(self, record: Dict[str, Any], parent_key: str = "") -> Dict[str, Any]:
+        """Flatten a record for CSV output.
+
+        Args:
+            record: Record to flatten
+            parent_key: Prefix for nested keys
+
+        Returns:
+            Flattened dictionary
+        """
+        result = {}
+
+        for key, value in record.items():
+            new_key = f"{parent_key}.{key}" if parent_key else key
+
+            if isinstance(value, dict):
+                result.update(self._flatten_record(value, new_key))
+            elif isinstance(value, list):
+                if not value:
+                    result[new_key] = ""
+                elif isinstance(value[0], dict):
+                    for i, item in enumerate(value):
+                        result.update(self._flatten_record(item, f"{new_key}[{i}]"))
+                else:
+                    result[new_key] = json.dumps(value)
+            else:
+                result[new_key] = value if value is not None else ""
+
+        return result
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