diff --git a/chunk.c b/chunk.c
new file mode 100644
index 0000000..7bb2fdd
--- /dev/null
+++ b/chunk.c
@@ -0,0 +1,177 @@
+#include "chunk.h"
+
+RegionID translateChunkToRegion(int x, int z);
+RegionID translateCoordsToRegion(double x, double y, double z);
+ChunkID translateCoordsToChunk(double x, double y, double z);
+int overwriteChunk(const char* regionFolder, ChunkID chunk, void* chunkData, size_t chunkLength);
+ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData);
+
+RegionID translateChunkToRegion(int x, int z) {
+    RegionID region;
+    region.x = x/CHUNKS_PER_REGION;
+    region.z = z/CHUNKS_PER_REGION;
+    return region;
+}
+
+RegionID translateCoordsToRegion(double x, double y, double z) {
+    ChunkID chunk = translateCoordsToChunk(x,y,z);
+    return translateChunkToRegion(chunk.x,chunk.z);
+}
+
+ChunkID translateCoordsToChunk(double x, double y, double z) {
+    ChunkID chunk;
+    chunk.x = x/BLOCKS_PER_CHUNK;
+    chunk.z = z/BLOCKS_PER_CHUNK;
+    return chunk;
+}
+
+int overwriteChunk(const char* regionFolder, ChunkID chunk, void* chunkData, size_t chunkLength) {
+    RegionID region = translateChunkToRegion(chunk.x,chunk.z);
+    ChunkID relativeChunk;
+    relativeChunk.x = chunk.x % 32;
+    relativeChunk.z = chunk.z % 32;
+
+    char* regionFilename = calloc(MAX_REGION_FILENAME_LENGTH + strlen(regionFolder),sizeof(char));
+    sprintf(regionFilename,"%s/r.%d.%d.mca.new",regionFolder,region.x,region.z);
+
+    if(access(regionFilename,R_OK | W_OK) == -1) {
+        fprintf(stderr,"Can't access file %s: %s\n",regionFilename,strerror(errno));
+        return -1;
+    }
+
+    int fd = open(regionFilename,O_RDWR);
+    if(fd == -1) {
+        fprintf(stderr,"Unable to open region file %s: %s\n",regionFilename,strerror(errno));
+        return -2;
+    }
+    free(regionFilename);
+
+    uint32_t chunkHeaderOffset;
+    if(pread(fd,&chunkHeaderOffset,sizeof(uint32_t),(relativeChunk.x + relativeChunk.z * CHUNK_OFFSET_LENGTH) * sizeof(uint32_t)) == -1) {
+        close(fd);
+        fprintf(stderr,"Unable to read chunk header offset: %s\n",strerror(errno));
+        return -3;
+    }
+    uint32_t totalChunkLength = (chunkHeaderOffset >> 24) * 4096;
+    chunkHeaderOffset = (__bswap_32(chunkHeaderOffset & 0x00FFFFFF) >> 8) * CHUNK_SECTOR_SIZE;
+    int pos = lseek(fd,chunkHeaderOffset,SEEK_SET);
+    if(pos == -1) {
+        close(fd);
+        fprintf(stderr,"Unable to seek to header offset: %s\n",strerror(errno));
+        return -4;
+    }
+
+    ChunkHeader header;
+    if(pread(fd,&header,sizeof(ChunkHeader),pos) <= 0) {
+        close(fd);
+        fprintf(stderr,"Unable to read chunk header: %s\n",strerror(errno));
+        return -5;
+    }
+    header.length = __bswap_32(header.length);
+
+    void* compressedChunk;
+    ssize_t compressedChunkLength = deflateGzip(chunkData,chunkLength,&compressedChunk,(header.compressionType == COMPRESSION_TYPE_ZLIB));
+    if(compressedChunkLength > totalChunkLength) {
+        // insert new 4096 blocks
+    }
+    header.length = __bswap_32((uint32_t)compressedChunkLength+1);
+    if(write(fd,&header,sizeof(ChunkHeader)) <= 0) {
+        close(fd);
+        free(compressedChunk);
+        fprintf(stderr,"Unable to read chunk header: %s\n",strerror(errno));
+        return -6;
+    }
+    ssize_t nWritten = 0;
+    size_t totalWritten = 0;
+
+    while((nWritten = write(fd,compressedChunk+totalWritten,compressedChunkLength-totalWritten))) {
+        if(nWritten == -1) {
+            if(errno == EINTR) {
+                continue;
+            }
+            fprintf(stderr,"Unable to write chunk: %s\n",strerror(errno));
+            close(fd);
+            free(compressedChunk);
+            return -7;
+        }
+        totalWritten += nWritten;
+    }
+    close(fd);
+    free(compressedChunk);
+    return 0;
+}
+
+ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData) {
+    RegionID region = translateChunkToRegion(chunk.x,chunk.z);
+    ChunkID relativeChunk;
+    relativeChunk.x = chunk.x % 32;
+    relativeChunk.z = chunk.z % 32;
+
+    char* regionFilename = calloc(MAX_REGION_FILENAME_LENGTH + strlen(regionFolder),sizeof(char));
+    sprintf(regionFilename,"%s/r.%d.%d.mca",regionFolder,region.x,region.z);
+
+    if(access(regionFilename,R_OK) == -1) {
+        fprintf(stderr,"Can't access file %s: %s\n",regionFilename,strerror(errno));
+        return -1;
+    }
+
+    int fd = open(regionFilename,O_RDONLY);
+    if(fd == -1) {
+        fprintf(stderr,"Unable to open region file %s: %s\n",regionFilename,strerror(errno));
+        return -2;
+    }
+    free(regionFilename);
+
+    uint32_t chunkHeaderOffset;
+    if(pread(fd,&chunkHeaderOffset,sizeof(uint32_t),(relativeChunk.x + relativeChunk.z * CHUNK_OFFSET_LENGTH) * sizeof(uint32_t)) == -1) {
+        close(fd);
+        fprintf(stderr,"Unable to read chunk header offset: %s\n",strerror(errno));
+        return -3;
+    }
+    chunkHeaderOffset = (__bswap_32(chunkHeaderOffset & 0x00FFFFFF) >> 8) * CHUNK_SECTOR_SIZE;
+
+    if(lseek(fd,chunkHeaderOffset,SEEK_SET) == -1) {
+        close(fd);
+        fprintf(stderr,"Unable to seek to header offset: %s\n",strerror(errno));
+        return -4;
+    }
+
+    ChunkHeader header;
+    if(read(fd,&header,sizeof(ChunkHeader)) <= 0) {
+        close(fd);
+        fprintf(stderr,"Unable to read chunk header: %s\n",strerror(errno));
+        return -5;
+    }
+    header.length = __bswap_32(header.length);
+    ssize_t chunkLength = header.length;
+    
+    void* compressedChunk = calloc(chunkLength,sizeof(char));
+    ssize_t nRead = 0;
+    size_t totalRead = 0;
+    
+    while((nRead = read(fd,compressedChunk+totalRead,chunkLength-totalRead))) {
+        if(nRead == -1) {
+            if(errno == EINTR) {
+                continue;
+            }
+            fprintf(stderr,"Unable to read chunk: %s\n",strerror(errno));
+            close(fd);
+            free(compressedChunk);
+            return -6;
+        }
+        totalRead += nRead;
+    }
+    close(fd);
+
+    void *decompressedChunk;
+    chunkLength = inflateGzip(compressedChunk,chunkLength,&decompressedChunk,(header.compressionType == COMPRESSION_TYPE_ZLIB));
+    
+    if(chunkLength <= 0) {
+        fprintf(stderr,"Error while decompressing chunk\n");
+        return -8;
+    }
+    free(compressedChunk);
+
+    *chunkData = decompressedChunk;
+    return chunkLength;
+}
\ No newline at end of file
diff --git a/chunk.h b/chunk.h
new file mode 100644
index 0000000..e369742
--- /dev/null
+++ b/chunk.h
@@ -0,0 +1,49 @@
+#ifndef _CHUNK_H
+#define _CHUNK_H
+
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdint.h>
+#include <string.h>
+#include <byteswap.h>
+
+#include "compression.h"
+
+#define BLOCKS_PER_CHUNK 16
+#define CHUNKS_PER_REGION 32
+#define CHUNK_OFFSET_LENGTH 32
+#define CHUNK_SECTOR_SIZE 4096
+
+// 58593 is the maximum number of regions containing 32 chunks in any direction
+// Thus, biggest filename is:
+// r.-58593.-58593.mca
+#define MAX_REGION_FILENAME_LENGTH 32 // Just to round up
+
+enum COMPRESSION_TYPE {
+    COMPRESSION_TYPE_GZIP = 1,
+    COMPRESSION_TYPE_ZLIB = 2
+};
+
+typedef struct RegionID {
+    int x;
+    int z;
+} RegionID;
+
+typedef struct ChunkID {
+    int x;
+    int z;
+} ChunkID;
+
+typedef struct __attribute__((packed)) ChunkHeader {
+    uint32_t length;
+    uint8_t compressionType;
+} ChunkHeader;
+
+ChunkID translateCoordsToChunk(double x, double y, double z);
+int overwriteChunk(const char* regionFolder, ChunkID chunk, void* chunkData, size_t chunkLength);
+ssize_t loadChunk(const char* regionFolder, ChunkID chunk, void** chunkData);
+
+#endif
\ No newline at end of file